Filed by: Columbia Banking System, Inc.

Pursuant to Rule 425 under the Securities Act of 1933

and deemed filed pursuant to Rule 14a-12

of the Securities Exchange Act of 1934

Subject Company: Pacific Premier Bancorp, Inc.

Commission File No.: 000-22193

This filing relates to the proposed transaction between Columbia Banking System, Inc. (“Columbia”) and Pacific Premier Bancorp, Inc. (“Pacific Premier”) pursuant to the Agreement and Plan of Merger, dated as of April 23, 2025, by and among Columbia, Pacific Premier and Balboa Merger Sub, Inc.

May 2025 Investor Presentation

2 Disclaimer FORWARD-LOOKING STATEMENTS This communication may contain certain forward-looking statements, including, but not limited to, certain plans, expectations, goals, projections, and statements about the benefits of the proposed business combination transaction between Columbia Banking System, Inc. (“Columbia”) and Pacific Premier Bancorp, Inc. (“Pacific Premier”) (the “Transaction”), the plans, objectives, expectations and intentions of Columbia and Pacific Premier, the expected timing of completion of the Transaction, and other statements that are not historical facts. Such statements are subject to numerous assumptions, risks, and uncertainties. All statements other than statements of historical fact, including statements about beliefs and expectations, are forward-looking statements. Forward-looking statements may be identified by words such as “expect,” “anticipate,” “believe,” “intend,” “estimate,” “plan,” “believe,” “target,” “goal,” or similar expressions, or future or conditional verbs such as “will,” “may,” “might,” “should,” “would,” “could,” or similar variations. The forward-looking statements are intended to be subject to the safe harbor provided by Section 27A of the Securities Act of 1933, Section 21E of the Securities Exchange Act of 1934, and the Private Securities Litigation Reform Act of 1995. Although there is no assurance that any list of risks and uncertainties or risk factors is complete, below are certain factors which could cause actual results to differ materially from those contained or implied in the forward- looking statements or historical performance: changes in general economic, political, or industry conditions, and in conditions impacting the banking industry specifically; uncertainty in U.S. fiscal, monetary and trade policy, including the interest rate policies of the Federal Reserve Board or the effects of any declines in housing and commercial real estate prices, high or increasing unemployment rates, continued or renewed inflation, the impact of proposed or imposed tariffs by the U.S. government or retaliatory tariffs proposed or imposed by U.S. trading partners that could have an adverse impact on customers or any recession or slowdown in economic growth particularly in the western United States; volatility and disruptions in global capital and credit markets; the impact of bank failures or adverse developments at other banks on general investor sentiment regarding the stability and liquidity of banks; changes in interest rates that could significantly reduce net interest income and negatively affect asset yields and valuations and funding sources, including impacts on prepayment speeds; competitive pressures among financial institutions and nontraditional providers of financial services, including on product pricing and services; concentrations within Columbia’s or Pacific Premier’s loan portfolio (including commercial real estate loans), large loans to certain borrowers, and large deposits from certain clients; the success, impact, and timing of Columbia’s and Pacific Premier’s respective business strategies, including market acceptance of any new products or services and Columbia’s and Pacific Premier’s ability to successfully implement efficiency and operational excellence initiatives; the nature, extent, timing, and results of governmental actions, examinations, reviews, reforms, regulations, and interpretations; changes in laws or regulations; the occurrence of any event, change or other circumstances that could give rise to the right of one or both of the parties to terminate the merger agreement to which Columbia and Pacific Premier are parties; the outcome of any legal proceedings that may be instituted against Columbia or Pacific Premier; delays in completing the Transaction; the failure to obtain necessary regulatory approvals (and the risk that such approvals may result in the imposition of conditions that could adversely affect the combined company or the expected benefits of the Transaction); the failure to obtain shareholder or stockholder approvals, as applicable, or to satisfy any of the other conditions to the closing of the Transaction on a timely basis or at all; changes in Columbia’s or Pacific Premier’s share price before closing, including as a result of the financial performance of the other party prior to closing, or more generally due to broader stock market movements, and the performance of financial companies and peer group companies; the possibility that the anticipated benefits of the Transaction are not realized when expected or at all, including as a result of the impact of, or problems arising from, the integration of the two companies or as a result of the strength of the economy and competitive factors in the areas where Columbia and Pacific Premier do business; certain restrictions during the pendency of the proposed Transaction that may impact the parties’ ability to pursue certain business opportunities or strategic Transactions; the possibility that the Transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; diversion of management’s attention from ongoing business operations and opportunities; potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the Transaction; the ability to complete the Transaction and integration of Columbia and Pacific Premier promptly and successfully; the dilution caused by Columbia’s issuance of additional shares of its capital stock in connection with the Transaction; and other factors that may affect the future results of Columbia and Pacific Premier. Additional factors that could cause results to differ materially from those described above can be found in Columbia’s Annual Report on Form 10-K for the year ended December 31, 2024, which is on file with the Securities and Exchange Commission (the “SEC”) (available here) and available on Columbia’s investor relations website, www.columbiabankingsystem.com, under the heading “SEC Filings,” and in other documents Columbia files with the SEC, and in Pacific Premier’s Annual Report on Form 10-K for the year ended December 31, 2024, which is on file with the SEC (available here) and available on Pacific Premier’s website, www.investors.ppbi.com, under the heading “SEC Filings” and in other documents Pacific Premier files with the SEC. All forward-looking statements speak only as of the date they are made and are based on information available at that time. Neither Columbia nor Pacific Premier assumes any obligation to update forward-looking statements to reflect circumstances or events that occur after the date the forward-looking statements were made or to reflect the occurrence of unanticipated events except as required by federal securities laws. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance on such statements.

3 Disclaimer (continued) IMPORTANT ADDITIONAL INFORMATION AND WHERE TO FIND IT In connection with the proposed Transaction, Columbia will file with the SEC a Registration Statement on Form S-4 that will include a Joint Proxy Statement of Columbia and Pacific Premier and a Prospectus of Columbia, as well as other relevant documents concerning the Transaction. Certain matters in respect of the Transaction involving Columbia and Pacific Premier will be submitted to Columbia’s and Pacific Premier’s shareholders or stockholders, as applicable, for their consideration. This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval, nor shall there be any sale of securities, in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. INVESTORS, COLUMBIA SHAREHOLDERS AND PACIFIC PREMIER STOCKHOLDERS ARE URGED TO READ THE REGISTRATION STATEMENT AND THE JOINT PROXY STATEMENT/PROSPECTUS REGARDING THE TRANSACTION WHEN THEY BECOME AVAILABLE AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC IN CONNECTION WITH THE TRANSACTION, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THOSE DOCUMENTS, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION. Shareholders or stockholders, as applicable, will be able to obtain a free copy of the definitive joint proxy statement/prospectus, as well as other filings containing information about the Transaction, Columbia and Pacific Premier, without charge, at the SEC’s website, www.sec.gov. Copies of the joint proxy statement/prospectus and the filings with the SEC that will be incorporated by reference in the joint proxy statement/prospectus can also be obtained, without charge, by directing a request to Columbia Banking System, Inc., Attention: Investor Relations, 1301 A Street, Tacoma, WA 98402-4200, (503) 727-4100 or to Pacific Premier Bancorp, Inc., Attention: Corporate Secretary, 17901 Von Karman Avenue, Suite 1200, Irvine, CA 92614, (949) 864-8000. PARTICIPANTS IN THE SOLICITATION Columbia, Pacific Premier, and certain of their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from Columbia shareholders or Pacific Premier stockholders in connection with the Transaction under the rules of the SEC. Information regarding Columbia’s directors and executive officers is available in the sections entitled “Directors, Executive Officers and Corporate Governance” and “Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters” in Columbia’s Annual Report on Form 10-K for the fiscal year ended December 31, 2024, which was filed with the SEC on February 25, 2025 (available here); in the sections entitled “Board Structure and Compensation,” “Compensation Discussion and Analysis,” “Compensation Tables,” “Information about Executive Officers,” “Beneficial Ownership of Directors and Executive Officers” and “Certain Relationships and Related Transactions” in Columbia’s definitive proxy statement relating to its 2025 Annual Meeting of Shareholders, which was filed with the SEC on April 3, 2025 (available here); and other documents filed by Columbia with the SEC. Information regarding Pacific Premier’s directors and executive officers is available in the sections entitled “Directors, Executive Officers and Corporate Governance” and “Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters” in Pacific Premier’s Annual Report on Form 10-K for the fiscal year ended December 31, 2024, which was filed with the SEC on February 28, 2025 (available here); in the sections entitled “Compensation of Non-Employee Directors,” “Security Ownership of Directors and Executive Officers,” “Certain Relationships and Related Transactions,” “Summary Compensation Table,” “Employment Agreements, Salary Continuation Plans, Severance, and Change-in-Control Payments,” and “Summary of Potential Termination Payments” in Pacific Premier’s definitive proxy statement relating to its 2025 Annual Meeting of Stockholders, which was filed with the SEC on April 7, 2025 (available here); and other documents filed by Pacific Premier with the SEC. To the extent holdings of Columbia common stock by the directors and executive officers of Columbia or holdings of Pacific Premier common stock by directors and executive officers of Pacific Premier have changed from the amounts held by such persons as reflected in the documents described above, such changes have been or will be reflected on Statements of Change in Ownership on Form 4 filed with the SEC. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the joint proxy statement/prospectus relating to the Transaction. Free copies of this document may be obtained as described in the preceding paragraph. NON-GAAP FINANCIAL MEASURES In addition to results presented in accordance with GAAP, this presentation contains certain non-GAAP financial measures. A reconciliation of GAAP to non-GAAP measures is included in the Appendix. The Company believes presenting certain non-GAAP financial measures provides investors with information useful in understanding our financial performance, our performance trends, and our financial position. We utilize these measures for internal planning and forecasting purposes, and operating pre-provision net revenue and operating return on tangible common equity are also used as part of our incentive compensation program for our executive officers. We, as well as securities analysts, investors, and other interested parties, also use these measures to compare peer company operating performance. We believe that our presentation and discussion, together with the accompanying reconciliations, provides a complete understanding of factors and trends affecting our business and allows investors to view performance in a manner similar to management. These non-GAAP measures should not be considered a substitution for GAAP basis measures and results, and we strongly encourage investors to review our consolidated financial statements in their entirety and not to rely on any single financial measure. Because non-GAAP financial measures are not standardized, it may not be possible to compare these financial measures with other companies’ non-GAAP financial measures having the same or similar names.

4 Columbia Banking System: A Franchise Like No Other Columbia at a Glance West-Focused Regional PowerhouseBusiness Bank of Choice ■In-market, relationship-based commercial TickerCOLB banking HeadquartersTacoma, Washington ■Attractive footprint in high-growth markets Offices~300 in eight states ■Full suite of deposit products and services with contemporary digital capabilities Assets$52 billion ■Expertise in treasury management, foreign exchange, and global cash management Loans$38 billion ■Expanding small business platform Deposits$42 billion ■Comprehensive and growing wealth advisory and trust businesses Common Equity (1) 10.6% ■Niche verticals include diverse agricultural, Tier 1 Capital Ratio healthcare, tribal banking, and equipment finance (1) Total Capital Ratio12.8% (1)Regulatory capital ratios are estimates pending completion and filing of Columbia’s regulatory reports. Financials as of March 31, 2025Corporate

5 Why Columbia? ■Our Business Bank of Choice strategy cultivates a granular, low-cost core deposit base ■Opportunity to gain share in California and growing metros in the West while increasing density in the Northwest ■Solid capital generation supports long-term organic growth and return to shareholders ■Strong credit quality is supported by a diversified, well-structured, and conservatively underwritten loan portfolio ■Compelling culture and Community Banking at Scale business model foster deep community ties while also attracting and retaining top banking talent ■Scaled western franchise is difficult to replicate and provides scarcity value

6 Operating in Large, Attractive Western Markets (1) (1)(1) Top Regional Bank in the NW (WA, OR, ID) Foothold in the WestEstablished Presence in Attractive Markets (population in millions)TotalNorthwest Northwest RankBank (HQ State)Assets ($B)Deposits ($B)Mkt Shr ■Our market share in the Northwest 1Bank of America (NC)$3,349$58 16.4 % stands with large national and super 4.1mm2.5mm0.8mm 2U.S. Bancorp (MN)676521 4.7 % regional banks, at nearly 10% 3JPMorgan (NY)4,358451 2.7 % 4Wells Fargo (CA)1,950401 1.3 % ■Our foothold in top western markets and 5 COLB (WA)7034 9.8 % scaled franchise provide us the Seattle, WAPortland, ORBoise, ID6KeyCorp (OH)189185 .2 % opportunity to increase share in 7WaFd (WA)2812 3.4 % California and Nevada California, Arizona, Colorado, and Utah 8Banner Corp. (WA)1611 3.0 % 12.8mm2.4mm2.4mm ■Densely populated metropolitan areas th(1) 5 Largest Bank HQ’d in our Footprint provide opportunity for our bankers to TotalEight-State Footprint take market share as we grow where RankBank (HQ State)Assets ($B)Deposits ($B)Mkt Shr businesses are growing Los Angeles, CASacramento, CALas Vegas, NV 1Wells Fargo (CA)$1,950$448 12.4 % 2Zions (UT)8859 1.7 % Other West ■Current household income in our 3Western Alliance (AZ)8365 1.8 % footprint is 106% of the national 4East West (CA)76521 .5 % 5.2mm3.0mm1.3mm average, and the five-year growth rate of 5 COLB (WA)70561 .6 % 9.0% compares favorably to 8.8% 6Banc of California (CA)34240 .7 % nationally 7WaFd (WA)2819 0.5 % 8FirstBank (CO)27240 .7 % Phoenix, AZDenver, COSalt Lake City, UT (1)Population, household income, and asset data sourced from S&P Global Market Intelligence. Total assets as of March 31, 2025. Deposits and market share data sourced from the Federal Deposit Insurance Corporation (“FDIC”) as of June 30, 2024 and adjusted to a pro forma basis for Columbia's acquisition of Pacific Premier Bancorp, Inc., which is expected to close in the second half of 2025, subject to the satisfaction of customary closing conditions, including regulatory and shareholder approvals. Columbia and Pacific Premier will operate as separate companies until closing and information contained herein about the combined company and on a pro forma basis is provided solely on an illustrative basis. Groups represent banks headquartered in the United States.

7 Acquisition of Pacific Premier Increases Scale and Opportunities (1) Adds Scale in Southern California and Increased Presence in NorthwestPro Forma Snapshot $70B$51B$57B AssetsLoansDeposits (2) Top 10 Market Share in Southern California Total% of RankBankDeposits ($mm)Franchise 1JPMorgan Chase$180,813 7.5 % 2Bank of America145,9947 .6 % 3Wells Fargo134,158 9.8 % (3) 4Royal Bank of Canada53,0625 .6 % 5U.S. Bancorp49,6299 .5 % 6East West Bancorp43,1907 2.0 % 7Citigroup42,6563 .3 % 8Axos Financial17,8439 2.2 % 9Bank of California17,743 61.6 % 10Pro Forma14,644 26.1 % 12Pacific Premier13,5099 2.4 % 51Columbia1,135 2.7 % (1)Financial data present Columbia and Pacific Premier on a combined pro forma basis as of March 31, 2025 and do not reflect purchase accounting adjustments. (2)Deposits and market share data sourced from S&P Global Market Intelligence as of June 30, 2024, and adjusted to a pro forma basis by S&P. Southern California defined as: Bakersfield-Delano, CA; El Centro, CA; Los Angeles-Long Beach-Anaheim, CA; Oxnard-Thousand Oaks- Ventura, CA; Riverside-San Bernardino-Ontario, CA; San Diego-Chula Vista-Carlsbad, CA; San Luis Obispo-Paso Robles, CA and Santa Maria-Santa Barbara, CA MSAs. (3)% of Franchise reflects percentage of Royal Bank of Canada’s deposits as of July 31, 2024.

8 Acquisition Increases Density throughout Our Footprint Enhances Density in the NorthwestImproves Competitive Position in CaliforniaAccelerates Growth in Expansion Markets Deposits ($mm)Market ShareDeposits ($mm)Market ShareDeposits ($mm)Market Share Pro Pro Pro Pro Pro Pro (1)(1)(1) MSAMarketCOLBFormaCOLBFormaMSAMarketCOLBFormaCOLBFormaMSAMarketCOLBFormaCOLBForma (2) Seattle$138,475$7,154$7,597 5.2 %5 .5 %Los Angeles$666,836$1,045$10,448 0.2 % 1.6 %Phoenix/Tucson$188,059$47$523<0.1% 0.3 % Portland61,8655,3285,4998 .6 %8 .9 %San Diego121,65534690<0.1%0 .6 %Denver111,173Branch opened in March 2025 (2) Boise16,5602202201 .3 %1 .3 %Inland Empire77,183 — 1,602 — %2 .1 %Las Vegas89,653 — 99 — % 0.1 % (2)(3) Spokane13,1283,8603,860 29.4 %2 9.4 %Central Coast22,743562,4930 .3 % 8.1 %Salt Lake City53,1071515<0.1%<0.1% (1)Deposits and market share data sourced from S&P Global Market Intelligence as of June 30, 2024, and adjusted to a pro forma basis by S&P. (2)Inland Empire defined as the Riverside-San Bernadino-Ontario, CA MSA; Central Coast defined as the Santa Maria-Santa Barbara, CA and San Luis Obispo-Paso Robles, CA MSAs; Phoenix/Tucson defined as Phoenix-Mesa-Chandler, AZ and Tucson, AZ MSAs. (3)Excludes specialty finance companies and banks with individual branches that have over $1 billion in deposits in the Salt Lake City MSA.

9 Acquisition Is Strategically Compelling and Financially Attractive ▪100% common stock, no capital raise required to support the transaction ▪Fixed exchange ratio; Pacific Premier stockholders will receive 0.9150 of a Columbia share for each Pacific Premier share Transaction (1) ▪Expected closing in the second half of 2025 Overview ▪The combined organization will operate under the unified brand of Columbia Bank ▪Accelerates Columbia’s Southern California expansion strategy by ~10 years ▪Creates a strategically cohesive regional powerhouse with ~$70 billion in assets Strategic ▪Enhances presence in core Northwest markets and expands presence in new growth markets (e.g., Phoenix) Rationale ▪Strong corporate fit and similar operating and credit philosophies limit execution risk ▪Top-decile peer pro forma profitability ratios (e.g., ROATCE, ROAA, efficiency) imply upside to Columbia’s valuation ▪Pacific Premier is comparatively overcapitalized with a 20.2% total RBC ratio and 17.0% CET1 ratio as of March 31, 2025 Financially (1) ▪14% 2026E EPS accretion with initial tangible book value dilution recovered in three years (crossover method) Attractive ▪Mark-to-market treatment enhances balance sheet restructuring flexibility ▪To reduce our combined pro forma asset sensitivity, we intend to purchase up to $3 billion of investment securities pre- closing, funded by short-term wholesale funding; we intend to offset this action post-closing by selling acquired securities Balance Sheet and repaying the short-term wholesale funding Preparation ▪We expect ~20 basis points of positive spread between securities yields and funding costs, resulting in slightly higher net interest income and ~8 basis points of net interest margin dilution for each $1 billion executed, subject to market conditions (1)See Appendix for pro forma financial assumptions and adjustments.

10 Leveraging Technology to Improve Collaboration and Performance Creating Operational Efficiencies Enhancing the Customer Experience Driving Revenue Generation ■Embracing AI capabilities to improve ■Differentiated small business and ■AI-powered Umpqua Smart Leads” associate productivitycommercial online banking platforms with support relationship banking and provide integrated technologies opportunities to generate fee income ■Continuing expansion of cloud through predictive analytics technologies and integrated banking ■Enhancing fraud protection and prevention through open APIsmeasures to minimize customer losses and ■Continued investment in new payment increase core fee income for the banktechnologies, including Real Time ■Developing support for human agents in Payments, integrated receivables and our contact center with virtual assistants■Updating our online account opening payables, and Zelle for Business process to make it easier and more ■Automating tasks and streamlining convenient for customers■Account aggregation and forecasting tools operations to enhance efficiency and integrated into online banking improve the customer experience; our goal ■Strengthening our bank security and risk is to be the most convenient bank for our management with advanced authentication ■Digital international banking solutions, associates (internally) and our customers technology to safeguard our customers including an online foreign exchange portal (externally)across digital platformsfor real time FX quotes and trades Our customer-focused technology stack incorporates resilient, scalable, and secure systems to support our Business Bank of Choice operating strategy. We embrace technology to not only create operational efficiencies, but also to support an elevated customer experience and to drive additional revenue opportunities through needs-based solutions. Many technology use cases support multiple goals: efficiency, customer satisfaction, and revenue growth.

FINANCIAL HIGHLIGHTS

12 First Quarter 2025 Highlights (1) ■Executed a successful small business and retail campaign using ReportedOperating bundled solutions for customers without promotional pricing. The $87 million$140 million Q1 2025 campaign brought $425 million in new deposits to the bank. Net IncomeNet Income ■Went live with Real Time Payments origination for customers in Q1 $151 million$212 million 2025, with a controlled rollout planned through 2025. (1) Pre-Provision Net RevenuePre-Provision Net Revenue ■Upgraded consumer bill pay within online banking to enhance the user interface and streamline our customers’ experience. $0.41$0.67 Earnings-per-Share - DilutedEarnings-per-Share - Diluted ■Treasury management and commercial card income increased 11% and 25%, respectively, for the trailing twelve-month period ended 0.68%1.10% March 31, 2025, relative to the period ended March 31, 2024. Return on AssetsReturn on Assets ■Opened a branch location in Denver, Colorado. The bank’s first retail 1.19%1.67%office in Colorado supports our commercial, wealth, trust, retail (1) PPNR Return on AssetsPPNR Return on Assetsbusiness, and healthcare banking teams already serving customers in the market. 6.73%10.87% ■Continued planning for additional branches slated to open in Return on EquityReturn on Equity targeted growth markets throughout our footprint during 2025, in 9.45%15.26%support of our customers and bankers. Return on Tangible Return on Tangible (1)■Two COLB directors recognized on Savoy’s 2024 Most Influential Common EquityCommon Equity Corporate Directors list. (1)Non-GAAP financial measure. A reconciliation to the comparable GAAP measurement for each is provided in the Appendix of this slide presentation.

13 Our Diversified Commercial Bank Business Model with a Strong Retail Network Supports our Granular, High-Quality Deposit Base (1) Enterprise-wide Deposit CompositionDeposits by CategoryCustomer Deposit Composition Commercial - Small Business, 19% Non-interest, 32% Demand, 20%Non-interest, 35% Demand, 19% Commercial, 28% Consumer, 38% Time, 10% Time, 14% Public & Other, 8% Money Market, 28% Money Market, 30% Savings, 6% Brokered, 7% Savings, 6% ■Deposits were $42 billion as of March 31, 2025 and represented by a granular base that is diversified by business line, industry, and geography. Our (1) average customer account balance is $36 thousand. ■Our use of public and brokered deposits as a source of funding beyond term debt impacts the composition of our enterprise-wide deposit portfolio. (1) We believe our customer deposit composition is more illustrative of the quality of Columbia’s core deposit franchise. Our bankers’ activity is geared toward protecting the quality of our relationship-based franchise while generating net customer balance growth to reduce the need for non-core funding sources over time. (1)Excludes all public, administrative, and brokered deposits, as detailed on the “Liquidity Overview” slide in the Appendix. Excluded balances accounted for 15% of total deposits as of March 31, 2025. This is a non-GAAP financial measure.

14 Securities Portfolio Overview Available-for-Sale Securities Portfolio Available-for-Sale Securities Portfolio as of March 31, 2025 Percentage at Gain / Loss as of March 31, 2025 % of Total Current Amortized Unrealized Unrealized AFS Effective ($ in millions)ParCostGainsLossesFair ValuePortfolioDurationBook Yield U.S. Treasuries $260 $257 $0 ($2) $255 3 %1.9 3.78 % U.S. Agencies 1,156 1,170 $4 ($56) 1,118 1 4 %3.22 .80 % Unrealized Gain, 36% Mortgage-backed securities - residential agency 2,962 2,773 $1 ($260) 2,514 31 %6.63 .22 % (1) Collateralized mortgage obligations 1,189 1,111 $8 ($91) 1,028 1 2 %5.8 3.45 % Unrealized Loss, 64% Obligations of states and political subdivisions 1,110 1,051 $3 ($33) 1,021 12 %4.4 3.43 % Commercial mortgage-backed securities - agency 2,435 2,321 $12 ($40) 2,293 2 8 %3.74 .63 % Total available for sale securities $9,113 $8,682 $29 ($482) $8,229 4.93 .61 % Percentage of current par9 5% 0% (5%) 90% ■The total available-for-sale (“AFS”) securities portfolio had a book yield of 3.61% and an effective duration of 4.9 as of March 31, 2025, compared to 3.64% and 5.1, respectively, as of December 31, 2024. ■As of March 31, 2025, 36% of the AFS securities portfolio (by fair value) was in an unrealized gain position and had a weighted average book yield of 4.71%. The remaining 64% of the portfolio was in an unrealized loss position and had a weighted average book yield of 3.04%. Note: Table may not foot due to rounding. (1)Portfolio includes $244 million in high-quality non-agency collateralized mortgage obligations (“CMO”) that were in a small unrealized gain position as of March 31, 2025 (amortized cost of $241 million). The remaining $784 million of the portfolio is comprised primarily of residential agency CMOs.

15 Loan Roll Forward Activity Three Months Ended March 31, 2025 $903 $37,681 $25$37,616 ($327) ($472) ($194) Beginning Balance New OriginationsNet Advances/ (Payments)PrepaymentsPayoffs or SalesOther¹Ending Balance (12/31/2024)(3/31/2025) Three Months Ended March 31, 2024 $772 $20$37,642 $37,442 ($74) ($342) ($176) Beginning Balance New OriginationsNet Advances/ (Payments)PrepaymentsPayoffs or SalesOther¹Ending Balance (12/31/2023)(3/31/2024) Note: Totals may not foot due to rounding. (1)Other reflects changes not otherwise defined. $ in millions$ in millions

16 Diversified, High Quality Loan and Lease Portfolio Portfolio Composition at March 31, 2025Owner Occupied CRE Mortgage •Portfolio average loan size of $1.1 million •Portfolio average loan size of $477,000 Multifamily, 15% •1Q25 average loan size of $2.1 million •1Q25 average loan size of $260,000 Other Loan •Portfolio average LTV of 55% •Portfolio average FICO of 761 and LTV of 61%Categories, 13% •1Q25 average LTV of 70% •1Q25 average FICO of 768 and LTV of 57% Non-OO CRE, 16% •Total delinquencies of 0.53% •Total delinquencies of 1.40% •Annualized net charge-off (recovery) rate of 0.01% •Annualized net charge-off (recovery) rate of 0.00% Mortgage, 16% Owner Occupied CRE, 14% Non-owner Occupied CRE Multifamily FinPac, 4% C&I, 22% •Portfolio average loan size of $1.7 million •Portfolio average loan size of $2.3 million •1Q25 average loan size of $2.7 million •1Q25 average loan size of $1.3 million •Portfolio average LTV of 51% and DSC of 1.88 •Portfolio average LTV of 54% and DSC of 1.57 •1Q25 average LTV of 52% and DSC of 1.22 •1Q25 average LTV of 68% and DSC of 1.16 •Total delinquencies of 1.19%Geographic Distribution at March 31, 2025 •Total delinquencies of 0.00% •Annualized net charge-off (recovery) rate of 0.00% •Annualized net charge-off (recovery) rate of 0.00% Other, 15% Puget Sound, 19% Commercial & IndustrialLease & Equipment Finance (FinPac) Southern CA, 15% WA Other, 8% •Portfolio average loan & lease size of $42,000 •Portfolio average loan size of $738,000 •1Q25 average loan & lease size of $56,000 •1Q25 average loan size of $634,000 •Portfolio average yield: ~10% Portland Metro, 13% •Total delinquencies of 0.91% Northern CA, 9% •Total delinquencies of 3.28% •Annualized net charge-off (recovery) rate of 0.57% •Annualized net charge-off (recovery) rate of 4.17% Bay Area, 7% OR Other, 14% Note: Portfolio statistics and delinquencies as of March 31, 2025. Annualized net charge-off rates for Q1 2025. Loan-to-value (“LTV”), FICO, and debt service coverage (“DSC”) ratios are based on weighted averages for portfolios where data are available. LTV represents average LTV based on most recent appraisal against updated loan balance. Totals may not foot due to rounding.

17 C&I and CRE Portfolio Composition (1)(1) C&I Portfolio Composition CRE Portfolio Composition $9.9 Billion as of March 31, 2025$17.3 Billion as of March 31, 2025 Agriculture, 8.7%Special Purpose, 7.2% Other, 10.2% Hotel/Motel, 4.1% Other Healthcare, 4.8% Contractors, 8.0% Retail, 11.2% Other, 11.0% Dentists, 6.8% Finance/Insurance, 7.7% Industrial, 16.6% Office, 16.1% Gaming, 8.4% Manufacturing, 6.8% Professional, 3.5% Wholesale, 7.9% Multifamily, 33.8% Public Admin, 6.0% Transportation/ Warehousing, 7.6% Rental & Leasing, 6.2% Support Services, 4.6% Retail, 2.8% (2) Commercial Line Utilization was 37% at March 31, 202546% Owner Occupied / 54% Non-Owner Occupied (1)C&I portfolio composition includes term, lines of credit & other, and leases & equipment finance balances. CRE portfolio composition includes non-owner occupied term and owner occupied term balances as well as multifamily balances. (2)Owner occupied and non-owner occupied disclosure relates to commercial real estate portfolio excluding multifamily loans.

18 Office Portfolio Details ■Loans secured by office properties Office Portfolio Metrics at March 31, 2025NNuummbbeerr ooff LLooaannss bbyy BBaallaannccee represented 8% of our total loan portfolio Average loan size$1.36 million 1,746 1,719 as of March 31, 2025. 1,579 Average LTV57% ■Our office portfolio is 41% owner DSC (non-owner occupied)1.81x occupied, 56% non-owner occupied, and % with guaranty (by $ / by #) 86% / 84% 3% construction. Dental and other Past due 30-89 days$19.2mm / 0.67% of office 448 444219 healthcare loans compose 20% of our Nonaccrual$10.0mm / 0.35% of office 74 7711office portfolio. 333893 787 664 Special mention$58.8mm / 2.03% of office ■The average loan size in our office <<<$$$111mmmmmm$$$111---555mmmmmm$$$555---111000mmmmmm$$$111000---222000mmmmmm$$$222000---333000mmmmmm>>>$$$333000mmmmmm Classified$82.2mm / 2.84% of office portfolio is $1.36 million. Delinquencies were at a very low level as of March 31, Repricing ScheduleMaturity ScheduleGeography 2025, and the majority of our loans Other, 9% contain a guaranty. 2026, 6% 2026, 3% ■Excluding floating rate loans, only 7% of 2027 & 2025, 5% After, 16% 2025, 4% our office portfolio reprices through 2026. S. CA, 19% Loans repricing in 2025 and 2026 have Puget Sound, 21% Floating Rate, 5% average balances of $0.8 million and $0.7 million, respectively. WA Other, 6% N. CA, 11% 2027 & Portland ■Properties located in suburban markets Fixed Rate¹, 72%After, 89% Metro, 12% secure the majority of our office portfolio, OR Other, 16% Bay Area, 6% as only 6% of non-owner occupied office loans are located in downtown core business districts. (1)Loans with a swap component are displayed as a fixed rate loan if the swap maturity is equal to the maturity of the loan. If the swap matures prior to the loan, the loan is displayed as adjustable with the rate resetting at the time of the swap maturity.

19 Continued Strong Credit Quality ■The remaining credit discount on loans of Allowance for Credit Losses ( ACL ) 1.36% 1.35% 1.33% 1.34%1.32% $57 million as of March 31, 2025 provides an additional 15 basis points of loss absorption when added to the ACL of 1.17%1.17%1.17% 1.16%1.16% $74 $69$65$60$57 $439 million. ■Net charge-offs in the FinPac portfolio $437$439$438$441$439 were $17 million in Q1 2025, down from Q1 2024Q2 2024Q3 2024Q4 2024Q1 2025 $19 million in Q4 2024, as improvement continues within the transportation sector ACL ($mm)Credit Discount ($mm)ACL / Total Loans and LeasesACL + Credit Discount / Total Loans and Leases of the portfolio. Net charge-offs excluding the FinPac portfolio were $13 million, or 0.14% of average bank loans, in Q1 2025, Provision Expense, Net Charge-Offs to Average Loans, and Nonperforming Assets to Total Assets compared to $6 million, or 0.07% of 0.47% average bank loans, in Q4 2024. The 0.35% 0.32%0.33% 0.32% increase reflects the partial charge-off of a loan with a previously established reserve. 0.32% 0.31% 0.30% 0.28%0.27% ■Nonperforming loans of $175 million as of $17.1$31.8$28.8$28.2$27.4 March 31, 2025 included $67 million of Q1 2024Q2 2024Q3 2024Q4 2024Q1 2025 loans with government guarantees. Provision Expense ($mm)Net Charge-Offs / Average Loans (annualized)Non-Performing Assets / Total Assets

20 ACL Reflects Strong Portfolio Credit Metrics Allowance for Credit Losses by Loan Segment Total ACL Remaining including Lease & Commercial Residential & Credit Discount Credit Discount (1)(1) ($ in thousands)CommercialEquipmentReal EstateHome EquityConsumerTotalon Loanson Loans Balance as of December 31, 2024 $130,286 $95,317 $160,345 $46,784 $8,065 $440,797 $60,443 $501,240 Q1 2025 Net Charge-offs (11,523) (16,752) (100) (205) (741) (29,321) Reserve Build (Release) 9,950 14,214 15,913 (12,418) (256) 27,403 Balance as of March 31, 2025 $128,713 $92,779 $176,158 $34,161 $7,068 $438,879 $56,831 $495,710 % of Loans and Leases Outstanding1 .56% 5 .64% 0 .90% 0 .43% 4.07% 1 .17% 1 .32% ■Our reserve coverage by loan segment and for the overall loan and lease portfolio reflects our robust underwriting criteria and ongoing, routine portfolio monitoring activities. For example, we stress applicable variables, such as interest rates, cash flows, and occupancy, at inception and loan review and limit borrower proceeds as a result. These factors contribute to lower LTVs and higher DSC ratios, which are taken into consideration in the estimation of our ACL. ■The quarter’s provision expense of $27 million reflects credit migration trends, charge-off activity, and changes in the economic forecasts used in credit models. We used components of Moody’s Analytics’ February 2025 consensus economic forecast to estimate our ACL as of March 31, 2025. (1)Total includes reserve for unfunded commitments of $17.4 million and $16.2 million as of March 31, 2025 and December 31, 2024, respectively.

21 Capital Management Regulatory Capital Ratios: Bank and Holding Company as of March 31, 2025Capital Ratios Continue to Trend Up 14.0%14.0% 12.8%12.8%12.8% 12.6% 12.5% 12.2% 12.0% 11.5%11.5% 12.0%12.0% 10.6% 10.6%10.6%10.5% 10.3% 10.0% 9.8% 10.0%9.0%10.0% 8.4% 8.0%8.0% 6.0%6.0% 4.0%4.0% 6.5% 9% 9% 12% Long-Term TargetLong-Term TargetLong-Term TargetLong-Term Target 2.0%2.0% —%—% Tier 1 LeverageCET1Tier 1 CapitalTotal Risk-Based3/31/20246/30/20249/30/202412/31/202403/31/2025 Umpqua BankColumbia Banking SystemCOLB: CET1 RatioCOLB: Total RBC Ratio ■Regulatory capital ratios declined during Q1 2023 as a result of the merger and the impact of rate-related asset discounts on capital. Our capital ratios have continued to increase on a quarterly basis post merger closing. ■We expect to organically generate capital above what is required to support prudent growth and our regular dividend, with excess capital driving ratios higher and providing flexibility to consider additional return to shareholders. Note: Umpqua Bank and Columbia Banking System, Inc. long-term capital ratio targets reflect a targeted excess level of capital above regulatory well-capitalized minimums inclusive of the capital conservation buffer (“CCB”) where applicable. The minimum capital ratios to be considered well capitalized inclusive of the CCB are 7.0%, 8.5%, and 10.5% for the common equity tier 1 (“CET1”) ratio, tier 1 capital ratio, and total risk-based capital ratio, respectively. The CCB does not apply to the tier 1 leverage ratio, which has a well-capitalized minimum level of 5.0%. All regulatory capital ratios as of March 31, 2025 are estimates pending completion and filing of Columbia’s and Umpqua Bank’s regulatory reports.

22 Net Interest Income and Net Interest Margin Net Interest Income and Net Interest Margin Net Interest Margin: Q4 2024 vs Q1 2025 3.64% $437 $430 $427 $423$4250.03%3.60% 0.07% (0.09)% (0.04)% (0.01)% 3.64% 3.60% 3.56%3.56% 3.52% Q1 2024Q2 2024Q3 2024Q4 2024Q1 2025 Q4 2024 LHFIInvest-CashDepositsTerm DebtQ1 2025 Net Interest Income ($ in millions)Net Interest Margin ReportedmentsReported ■Net interest margin decreased 4 basis points from the prior quarter to 3.60% for Q1 2025, as lower earning asset yields were only partially offset by lower funding costs. ■The cost of interest-bearing deposits decreased 14 basis points from the prior quarter to 2.52% for Q1 2025, which compares to 2.51% for the month of March and 2.50% as of March 31, 2025. ■The cost of interest-bearing liabilities decreased 18 basis points from the prior quarter to 2.80% for Q1 2025, which compares to 2.76% for the month of March and 2.74% as of March 31, 2025. (1)Chart Abbreviations: “LHFI” = loans held for investment.

23 Interest Rate Sensitivity (1) Interest Rate Simulation Impact on Net Interest Income at March 31, 2025 Floors: Floating and Adjustable Rate Loans at March 31, 2025 RampShock (5)(5)(5) ($ in millions)No FloorAt FloorAbove FloorTotal Year 1Year 2Year 1Year 2 Floating$8,894$316$4,319$13,529 Up 200 basis points(0.7)%0.8%(1.1)%2.4% Adjustable1,5521359,54711,234 Up 100 basis points(0.3)%0.4%(0.5)%1.2% Down 100 basis points0.3%(0.6)%0.4%(1.5)%Total$10,446$451$13,866$24,763 Down 200 basis points1.0%(1.3)%1.1%(3.2)% % of Total42%2%56%100% Down 300 basis points1.9%(2.3)%1.7%(5.6)% Select Asset and Liability Maturity and Repricing Schedules (in Months) at March 31, 2025Downward Rate Change to Move to Floor at March 31, 2025 (3) ($ in millions)<=34 to 67 to 1213 to 2425 to 3636+Total% Total ($ in millions)Floating LoansAdjustable LoansAbove Floor Total Loans <25 basis points$19$36$55 (2) Fixed (maturity)$360$170$258$707$1,219$10,515$13,22935% 26 to 50 basis points11463177 (2) Floating (repricing)13,529—————13,52936% 51 to 75 basis points6249111 Adjustable (repricing)6673095221,5091,2356,99211,23430% 76 to 100 basis points12473197 Total Loans $14,556$479$780$2,216$2,454$17,507$37,992100% 101 to 125 basis points35102137 (4) Time deposits (maturity)$3,536$1,376$921$140$15$14$6,002 126 to 150 basis points52123175 (4) Average rate4.10%3.81%3.44%1.80%0.29%0.27%3.86% >150 basis points3,9139,10113,014 Term debt (maturity)$2,550$—$—$—$—$—$2,550 Total$4,319$9,547$13,866 Average rate4.47%4.47% Note: Tables may not foot due to rounding. Loan totals on this slide do not include purchase accounting adjustments. Deferred fees and costs also drive variances between loan totals on this slide and loan totals in the earnings press release. (1)For the scenarios shown, the interest rate simulations assume a parallel and sustained shift in market interest rates ratably over a twelve-month period (ramp) or immediately (shock). The simulation repricing betas applied to interest-bearing deposits in the rising rate and declining rate scenarios are 55% and 54%, respectively, for March 31, 2025. Additional data related to interest rate simulations are available in Columbia’s Form 10-K for the fiscal year ended December 31, 2024. (2)Commercial tranche loans that mature in one month are included in the floating rate loan category, not the fixed rate loan category, as these loans reprice in a manner similar to floating rate loans. (3)Floating rate loans are indexed to prime (8% of the total loan portfolio) and 1-month underlying interest rates (28% of the total loan portfolio). When adjustable rate loans reprice, they are indexed to interest rates that span 1-month tenors to 10-year tenors as well as the prime rate; the most prevalent underlying index rates are 6-month tenors (17% of the total loan portfolio) and 5-year tenors (6% of the total loan portfolio). (4)Time deposits maturing in 3 months or less include $1.5 billion in customer CDs at an average rate of 3.91% and $2.0 billion in brokered CDs at an average rate of 4.38%. (5)Loans were grouped into three buckets: (1) No Floor: no contractual floor on the loan; (2) At Floor: current rate = floor; (3) Above Floor: current rate exceeds floor. The amount above the floor was based on the current margin plus the current index assuming the loan repriced on March 31, 2025. The adjustable loans may not reprice until well into the future, depending on the timing and size of interest rate changes.

24 Longer-Term Balance Sheet Optimization Opportunities Deposit and Funding Repricing Betas During Current Rate Cycle Opportunity to Strategically Reposition Balance Sheet Over Time Cost of: Effective Fed Funds Rate Interest- Bearing Total DepositsTotal Funding Three Months Ended(Daily Avg.) Deposits (1) December 31, 20210.08%0.10%0.05%0.09% Relationship (1) $38B$46B banking December 31, 20223.65%0.62%0.35%0.51% Relationship Lending & Core Deposit Franchise supports December 31, 20235.33%2.54%1.63%2.05% Other Core Banking & Capital strong core June 30, 20245.33%2.97%2.01%2.34% Franchise franchise Variance: Q2 2024 less Q4 20215.25%2.87%1.96%2.25% value Repricing Betas: Rising Rate Cycle55%37%43% December 31, 20244.66%2.66%1.80%2.09% $8B Securities Opportunity March 31, 20254.33%2.52%1.72%1.99% to reduce $6B Wholesale Funding $2B SFR / $4B MF transactional Variance: Q1 2025 less Q2 2024(1.00)%(0.45)%(0.29)%(0.35)% assets and AssetsLiabilities + Equity Repricing Betas: Decling Rate Cycle-to-Date45%29%35% liabilities ■Our relationship-based lending verticals and a strong core deposit base remain the cornerstone of our franchise. Past transactional lending and the wholesale sources that fund these assets have muted the balance sheet’s profitability, but they have not diluted the quality of our core franchise. ■Current interest rates make outright asset sales unattractive given a lengthy payback period. However, longer term, any decline in rates would reduce or (2) potentially eliminate the drag on earnings as balances organically decline or are sold opportunistically. ■Post-closing, we expect to have increased flexibility for repositioning, as Pacific Premier’s balance sheet will be marked to fair value at closing. (1)Deposit and funding repricing beta data present combined company results as if historical Columbia and historical Umpqua Holdings Corporation were one company for all periods through December 31, 2022; subsequent time periods present data on a legal basis given the merger. The beta presentation is calculated in this manner for comparison purposes. (2)While asset classes, like transactional loans within our single-family (“SFR”) and multifamily (“MF”) portfolios, have been identified as potential sources for asset sales if interest rates were to decline further, assets have not been identified for sale.

25 Non-Interest Income For the Quarter Ended Q1 2025 Highlights (compared to Q4 2024) ($ in millions)Q1 2025Q4 2024Q3 2024Q2 2024Q1 2024 ■Our Business Bank of Choice strategy Service charges on deposits $19.3 $18.4 $18.5 $18.5 $16.1 incorporates a collaborative team Card-based fees 12.6 14.6 14.6 14.7 13.2 approach to deliver needs-based solutions to our customers, which deepens Financial services and trust revenue 5.2 5.3 5.1 5.4 4.5 relationships and provides growth in Residential mortgage banking revenue, net 9.3 7.0 6.7 5.8 4.6 sustainable core fee income. Our trends Gain (loss) on equity securities, net 1.7 (1.4) 2.3 0.3 (1.6) reflect a growing contribution from Gain (loss) on loan and lease sales, net 0.1 (1.7) 0.2 (1.5) 0.2 treasury management, card activity, BOLI income 4.9 4.7 4.7 4.7 4.6 financial services and trust, and other Other income product revenue over the trailing 12 (1) Other commercial product revenue $3.2 $2.0 $2.9 $2.6 $2.3 months. Q1 2025 also included a Commercial servicing revenue 0.4 0.6 0.5 0.2 0.6 recategorization from card-based fees Loan-related fees 3.6 3.4 3.3 4.1 3.7 into service charges on deposits. Change in fair value of certain loans held for 7.0 (7.4) 9.4 (10.1) (2.4) ■Fair value changes in certain loans carried investment at fair value, in combination with the Misc. income 0.6 0.6 1.6 (0.4) 3.3 swap derivative gain (loss), increased non- Swap derivative (loss) gain (1.5) 3.6 (3.6) 0.4 1.2 interest income by $6 million, compared to a $4 million reduction in Q4 2024. These items are captured in other income. Note: Tables may not foot due to rounding. (1)Other commercial product revenue includes swaps, syndication, and international banking revenue, which are captured in “other income” on the income statement. Other income statement line items, like card-based fees, include other sources of commercial product revenue.

26 Non-Interest Expense Non-Interest Expense ( NIE )Non-Interest Expense: Q4 2024 vs Q1 2025 $66.9$340.1 $340.1 $1.8 $1.5 $4.3 $266.6 $(1.0) $287.5 $279.2 $276.9 $271.4 $270.1 $268.4 $266.6 $263.5 $262.5 Q1 2024Q2 2024Q3 2024Q4 2024Q1 2025 Q4 2024 Payroll Software Legal FeesMisc. OtherNon-Q1 2025 GAAP Non-Interest ExpenseOperating Non-Interest Expense¹ NIETaxesCostsoperating¹NIE ■Non-interest expense in Q1 2025 increased $74 million from the prior quarter to $340 million, primarily due to a $55 million accrual related to a legal (1) settlement and $15 million of severance expense. Operating non-interest expense increased $7 million from the prior quarter to $270 million, (2) primarily due to higher payroll taxes and elevated legal expense separate from the legal settlement. ■Our cost-conscious culture provides expense offsets to continued investment in customer-focused technology, experienced bankers, and strategic locations. These investments create operational efficiency and bring additional revenue opportunities to the bank in support of our Business Bank of Choice strategy. (1)Non-GAAP financial measure. A reconciliation to the comparable GAAP measurement is provided at the end of this slide presentation. Non-operating expense items include merger and restructuring expense, exit and disposal costs, an FDIC special assessment, and the legal settlement. These items are detailed in the “Non-GAAP Reconciliation” section of the Appendix. (2)During Q1 2025, Columbia accrued $55 million related to a legal settlement that was disclosed in a Form 8-K filed with the SEC on March 27, 2025. $ in millions $ in millions

APPENDIX

28 Liquidity Overview Select Balance Sheet ItemsTotal Off-Balance Sheet Liquidity Available at March 31, 2025 Sequential Gross Net Three Months EndedQuarter Change($ in millions)AvailabilityUtilizationAvailability ($ in millions)Q1 2025Q4 2024Q1 2024Q1 2025FHLB lines $11,101 $2,596 $8,504 Commercial deposits $11,920 $11,787 $11,206 $133 Federal Reserve Discount Window 5,937 — 5,937 Small business deposits 8,104 7,886 8,103 218 Uncommitted lines of credit 600 — 600 Consumer deposits 15,982 15,893 16,241 89 Total off-balance sheet liquidity $17,637 $2,596 $15,041 Total customer deposits 36,006 35,566 35,550 440 Public deposits - non-interest bearing 697 636 645 61 Total Available Liquidity at March 31, 2025 ($ in millions) Public deposits - interest bearing 2,353 2,351 2,285 2 Total off-balance sheet liquidity (available lines of credit): $15,041 Total public deposits 3,050 2,987 2,930 63 Cash and equivalents, less reserve requirement 1,852 Excess bond collateral 2,073 Administrative deposits 173 137 136 36 Total available liquidity $18,966 Brokered deposits 2,989 3,031 3,090 (42) TOTAL AVAILABLE LIQUIDITY AS A PERCENTAGE OF: Total deposits $42,218 $41,721 $41,706 $497 Assets of $51.5 billion at March 31, 2025 37 % Deposits of $42.2 billion at March 31, 2025 45 % Term debt $2,550 $3,100 $3,900 ($550) Uninsured deposits of $14.5 billion at March 31, 2025 1 31 % Cash & cash equivalents $2,073 $1,878 $2,201 $194 Available-for-sale securities $8,229 $8,275 $8,617 ($46) Loans and leases $37,616 $37,681 $37,642 ($65) ■Customer deposits increased $440 million during Q1 2025, as small business campaigns and successful commercial customer balance generation offset anticipated seasonal customer cash usage earlier in the quarter. ■Customer deposit growth was used to help pay down $550 million in FHLB Advances and $42 million of brokered deposits during Q1 2025. Note: Tables may not foot due to rounding.

29 Summary Income Statements For the Quarter Ended Q1 2025 Highlights (compared to Q4 2024) ($ in millions, except per-share data) Q1 2025Q4 2024Q3 2024Q2 2024Q1 2024 ■Net interest income decreased by $12 Net interest income before provision $425.0 $437.4 $430.2 $427.4 $423.4 million, largely due to lower accretion Provision for credit losses 27.4 28.2 28.8 31.8 17.1 income from the investment securities Net interest income after provision 397.6 409.2 401.4 395.6 406.2 portfolio. Non-interest income 66.4 49.7 66.2 44.7 50.4 ■Non-interest income increased by $17 Non-interest expense 340.1 266.6 271.4 279.2 287.5 million due to the quarterly fluctuation in Income before provision for income taxes 123.8 192.3 196.3 161.1 169.1 cumulative fair value accounting and Provision for income taxes 37.2 49.1 50.1 40.9 45.0 hedges, which drove $15 million of the change. Income was also higher due to a Net income $86.6 $143.3 $146.2 $120.1 $124.1 loss on loan sales in Q4 2024 that did not Earnings per share, diluted $0.41 $0.68 $0.70 $0.57 $0.59 repeat. (1) Operating non-interest expense $270.1 $263.5 $268.4 $262.5 $276.9 ■Non-interest expense increased by $74 (1) Pre-provision net revenue $151.3 $220.5 $225.0 $192.9 $186.2 million, primarily due to a legal settlement (1) Operating pre-provision net revenue $211.8 $229.2 $221.4 $219.4 $200.7 and severance expense, as well as (1) Operating net income $139.8 $149.7 $143.5 $140.0 $134.9 seasonally higher payroll taxes. (1) Operating earnings per share, diluted $0.67 $0.71 $0.69 $0.67 $0.65 ■Provision expense of $27 million compares to $28 million in the prior quarter. Note: Tables may not foot due to rounding. (1)Non-GAAP financial measure. A reconciliation to the comparable GAAP measurement is provided at the end of this slide presentation.

30 Summary Period-End Balance Sheets ($ in millions, except per-share data)Q1 2025Q4 2024Q3 2024Q2 2024Q1 2024 Q1 2025 Highlights (compared to Q4 2024) ASSETS: ■Loan balances decreased slightly in Q1 Total assets $51,519.3 $51,576.4 $51,908.6 $52,047.5 $52,224.0 2025, due to higher prepayment and Interest bearing cash and temporary investments 1,481.4 1,381.6 1,519.7 1,553.6 1,760.9 payoff activity. Loan origination volume Investment securities available for sale, fair value 8,228.8 8,274.6 8,676.8 8,503.0 8,616.5 was down seasonally from Q4 2024, but up Loans and leases, gross 37,616.1 37,680.9 37,503.0 37,710.0 37,642.4 17% from Q1 2024, as growing momentum Allowance for credit losses on loans and leases (421.5) (424.6) (420.1) (418.7) (414.3) during 2024 carried through into 2025. Goodwill and other intangibles, net 1,485.5 1,513.5 1,542.5 1,571.6 1,600.8 ■Total deposits increased $497 million as LIABILITIES AND EQUITY: strong customer deposit growth in March Deposits 42,217.7 41,720.7 41,514.7 41,523.3 41,706.2 more than offset seasonal balance declines Securities sold under agreements to repurchase 192.4 236.6 183.8 197.9 213.6 earlier in the quarter. Customer deposit Borrowings 2,550.0 3,100.0 3,650.0 3,900.0 3,900.0 growth was used to help pay down $550 Total shareholders' equity 5,237.8 5,118.2 5,273.8 4,976.7 4,957.2 million in FHLB Advances and $42 million RATIOS AND PER-SHARE METRICS: of brokered deposits during Q1 2025. Loan to deposit ratio 8 9.1% 9 0.3% 9 0.3% 9 0.8% 90.3% ■Book value and tangible book value Book value per common share $24.93 $24.43 $25.17 $23.76 $23.68 increased 2.0% and 3.8%, respectively, due (1) Tangible book value per common share $17.86 $17.20 $17.81 $16.26 $16.03 to an interest rate-driven decrease in Common equity to assets ratio1 0.2% 9.9% 10.2% 9 .6% 9 .5% accumulated other comprehensive loss. (1) Tangible common equity to tangible assets ratio 7.5% 7 .2% 7 .4% 6 .7% 6.6% Book value and tangible book value increased 5.3% and 11.4%, respectively, from March 31, 2024. Note: Tables may not foot due to rounding. (1)Non-GAAP financial measure. A reconciliation to the comparable GAAP measurement is provided in the appendix of this slide presentation.

31 PPBI Acquisition: Transaction Summary ▪100% common stock, no capital raise required to support the transaction Structure & ▪Fixed exchange ratio; Pacific Premier stockholders will receive 0.9150 of a Columbia share for each Pacific Premier share Consideration ▪Pro forma ownership: 70% Columbia / 30% Pacific Premier (1) ▪Implied value per Pacific Premier share: $20.83 ▪Implied aggregate transaction value: $2.0 billion Implied Transaction▪Price / Tangible Book Value per Share: 0.99x ▪Price / LTM GAAP EPS: 13.7x Value & (1) ▪Price / 2026E Consensus EPS: 13.5x Multiples ▪Price / 2026E Consensus EPS + After-Tax Cost Savings: 8.4x ▪Three Pacific Premier directors invited to join the Columbia board of directors Board of Directors, ▪Columbia executive leadership team remains intact Management & ▪The combined organization will operate under the unified brand of Columbia Bank Company Name ▪Subject to receipt of approvals from Columbia and Pacific Premier shareholders and regulatory approvals Expected ▪Expected closing in the second half of 2025 Closing Note: Assumes 97,069,001 Pacific Premier common shares outstanding, 33,604 outstanding options with a weighted average exercise price of $20.71, and 525,897 other dilutive securities not included in shares outstanding. (1)Based on closing price of Columbia common stock of $22.77 as of April 22, 2025.

32 PPBI Acquisition: Key Pro Forma Financial Assumptions ▪Consensus earnings estimates for Columbia and Pacific Premier Standalone Earnings ▪Estimated $127 million of full run-rate cost savings, or 30% of Pacific Premier’s noninterest expense Synergies▪Cost savings realization expected to be 75% in 2026 and 100% thereafter ▪Significant revenue enhancements expected, but not included in announced financial metrics ▪$145 million after-tax, 100% realized at or prior to closing for illustrative purposes One-Time Costs ▪$449 million write-down on Pacific Premier’s gross loans, or 3.6% of its projected gross loans at closing (accreted over remaining life of loans) ▪$327 million write-down of held-to-maturity securities (accreted over remaining life of securities) Fair Value and ▪$91 million write-down of available-for-sale securities (no impact to tangible common equity at close, accreted over remaining life of securities) Interest Rate ▪$25 million reversal of existing mark on Pacific Premier acquired loans (reversal of associated accretion over remaining life of acquired loans) Marks (Pre-Tax) ▪$12 million write-up to fixed assets (depreciated over the remaining life of those assets) ▪$11 million write-up of time deposits (amortized over the remaining life of time deposits) (1) ▪$96 million pre-tax write-down, or 0.8% of Pacific Premier’s projected gross loans at closing (equal to 3.5x non-performing loans) ◦$48 million, or 50% of the total gross credit mark, allocated to purchase credit deteriorated (“PCD”) loans Credit Marks / ◦$48 million, or 50% of the total gross credit mark, allocated to non-PCD loans (accreted into earnings over remaining life of loans) CECL Impact ▪Day two CECL reserve of $48 million, equal to the mark on non-PCD loans ▪Core deposit intangible of 3.3% of Pacific Premier’s core deposits (amortized over 10 years using sum-of-years digits) CDI & ▪Pacific Premier to call its $275 million of outstanding subordinated debt prior to transaction closing Other Assumptions (1)Reflects Pacific Premier’s non-performing loans as of March 31, 2025.

33 PPBI Acquisition: Pro Forma Adjustments Summary Tangible Book Value per Share ReconciliationGoodwill Reconciliation Dollar values in millions, except per share amounts Dollar values in millions, except per share amounts Deal Value $2,033 Columbia Tangible Book Value per Share at Closing$19.14 Pacific Premier Common Equity at Closing $2,970 Columbia Common Equity at Closing $5,430 Existing Intangibles (924) Deal Value 2,033 DTL Related to Intangibles 6 Pacific Premier Unamortized Subordinated Debt Offering Expenses (2) (1) Purchase Accounting Adjustments Transaction Expenses (146) HTM Investment Securities ($327) Pro Forma Common Equity at Closing 7,315 Gross Loans (544) Columbia Intangible Assets at Closing 1,408 Loan Loss Reserve Reversal 168 Goodwill Generated 177 Acquired Loan Mark Reversal 25 CDI Generated 416 Fixed Assets 12 Pro Forma Intangibles at Closing 2,001 Total Purchase Accounting Adjustments: Assets (666) Deferred Tax Asset / (Liability) 166 Net Impact of CECL Reserve on Acquired Loans (36) Time Deposits (11) Pro Forma Tangible Common Equity at Closing $5,278 Total Purchase Accounting Adjustments: Liabilities (11) Deferred Tax Asset / (Liability) 3 Columbia Common Shares Outstanding at Closing210,112,415 Pacific Premier Adjusted Tangible Equity at Closing $1,544 Shares to Be Issued to Pacific Premier Shareholders88,368,619 Implied Premium $489 Pro Forma Common Shares Outstanding298,481,034 Premium Allocation Pro Forma Tangible Book Value per Share$17.68 Core Deposit Intangible $416 Deferred Tax Asset / (Liability) (104) Net CDI Allocation $312 Goodwill Allocation $177 (1)Positive numbers are benefits to equity; negative numbers are detriments to equity.

34 PPBI Acquisition: Pro Forma Adjustments Summary (continued) 2026E Earnings per Share Reconciliation2027E Earnings per Share Reconciliation Dollar values in millions, except per share amountsDollar values in millions, except per share amounts 2026E Earnings per Share Reconciliation2027E Earnings per Share Reconciliation Columbia Net Income (Median Consensus Estimate) $600 Columbia Net Income (Median Consensus Estimate) $630 Pacific Premier Net Income (Median Consensus Estimate) 150 Pacific Premier Net Income (Median Consensus Estimate) 176 After-Tax Transaction AdjustmentsAfter-Tax Transaction Adjustments Cost Savings (75% Realization) $69 Cost Savings (100% Realization) $96 Accretion from Interest Rate Marks 184 Accretion from Interest Rate Marks 135 Accretion from Non-PCD Credit Mark 15 Accretion from Non-PCD Credit Mark 11 New Intangible Amortization (57) New Intangible Amortization (51) Other Adjustments (2) Other Adjustments 1 Columbia Pro Forma Net Income $961 Columbia Pro Forma Net Income $999 Columbia 2026E Pro Forma EPS$3.24Columbia 2027E Pro Forma EPS$3.44 Columbia Standalone EPS$2.85Columbia Standalone EPS$3.00 2026E EPS Accretion to Columbia ($)$0.392027E EPS Accretion to Columbia ($)$0.44 2026E EPS Accretion to Columbia (%)14%2027E EPS Accretion to Columbia (%)15%

35 Non-GAAP Reconciliation: Tangible Capital ($ in thousands, except per-share data)3/31/202512/31/20249/30/20246/30/20243/31/2024 Total shareholders' equitya $5,237,809 $5,118,224 $5,273,828 $4,976,672 $4,957,245 Less: Goodwill 1,029,234 1,029,234 1,029,234 1,029,234 1,029,234 Less: Other intangible assets, net 456,269 484,248 513,303 542,358 571,588 Tangible common shareholders’ equityb 3,752,306 3,604,742 3,731,291 3,405,080 3,356,423 Total assetsc $51,519,266 $51,576,397 $51,908,599 $52,047,483 $52,224,006 Less: Goodwill 1,029,234 1,029,234 1,029,234 1,029,234 1,029,234 Less: Other intangible assets, net 456,269 484,248 513,303 542,358 571,588 Tangible assetsd $50,033,763 $50,062,915 $50,366,062 $50,475,891 $50,623,184 Common shares outstanding at period ende 210,112 209,536 209,532 209,459 209,370 Total shareholders' equity to total assets ratioa / c1 0.17 %9 .92 %1 0.16 %9 .56 %9 .49 % Tangible common equity to tangible assets ratiob / d7 .50 %7 .20 % 7.41 % 6.75 %6 .63 % Book value per common sharea / e $24.93 $24.43 $25.17 $23.76 $23.68 Tangible book value per common shareb / e $17.86 $17.20 $17.81 $16.26 $16.03

36 Non-GAAP Reconciliation: Adjustments and Average Balances For the Quarter Ended ($ in thousands)3/31/202512/31/20249/30/20246/30/20243/31/2024 Non-Interest Income Adjustments Gain (loss) on sale of debt securities, net$ 4 $ 10 $ 3 $ (1) $ 12 Gain (loss) on equity securities, net 1,702 (1,424) 2,272 325 (1,565) (Loss) gain on swap derivatives (1,494) 3,642 (3,596) 424 1,197 Change in fair value of certain loans held for investment 7,016 (7,355) 9,365 (10,114) (2,372) Change in fair value of MSR due to valuation inputs or assumptions (983) 7,414 (6,540) 1,238 3,117 MSR hedge gain (loss) 3,212 (7,819) 5,098 (1,611) (4,271) Total non-interest income adjustmentsa$ 9,457 $ (5,532) $ 6,602 $ (9,739) $ (3,882) Non-Interest Expense Adjustments Merger and restructuring expense$ 14,379 $ 2,230 $ 2,364 $ 14,641 $ 4,478 Exit and disposal costs 661 872 631 1,218 1,272 FDIC special assessment — — — 884 4,848 Legal settlement 55,000 — — — — Total non-interest expense adjustmentsb$ 70,040 $ 3,102 $ 2,995 $ 16,743 $ 10,598 Average Assetsn$ 51,452,608 $ 51,588,231 $ 52,009,017 $ 51,981,555 $ 52,083,973 Less: Average goodwill and other intangible assets, net 1,501,590 1,528,431 1,559,696 1,588,239 1,619,134 Average tangible assetso$ 49,951,018 $ 50,059,800 $ 50,449,321 $ 50,393,316 $ 50,464,839 Average common shareholders’ equityp$ 5,216,555 $ 5,226,290 $ 5,118,592 $ 4,908,239 $ 4,985,875 Less: Average goodwill and other intangible assets, net 1,501,590 1,528,431 1,559,696 1,588,239 1,619,134 Average tangible common equityq$ 3,714,965 $ 3,697,859 $ 3,558,896 $ 3,320,000 $ 3,366,741 Weighted average basic shares outstandingr 208,800 208,548 208,545 208,498 208,260 Weighted average diluted shares outstandings 210,023 209,889 209,454 209,011 208,956

37 Non-GAAP Reconciliation: Income Statements For the Quarter Ended ($ in thousands)3/31/202512/31/20249/30/20246/30/20243/31/2024 Net interest income c$ 424,995 $ 437,373 $ 430,218 $ 427,449 $ 423,362 Non-interest income (GAAP)d$ 66,377 $ 49,747 $ 66,159 $ 44,703 $ 50,357 Less: Non-interest income adjustmentsa (9,457) 5,532 (6,602) 9,739 3,882 Operating non-interest income (non-GAAP)e$ 56,920 $ 55,279 $ 59,557 $ 54,442 $ 54,239 Revenue (GAAP)f=c+d$ 491,372 $ 487,120 $ 496,377 $ 472,152 $ 473,719 Operating revenue (non-GAAP)g=c+e$ 481,915 $ 492,652 $ 489,775 $ 481,891 $ 477,601 Non-interest expense (GAAP)h$ 340,122 $ 266,576 $ 271,358 $ 279,244 $ 287,516 Less: Non-interest expense adjustmentsb (70,040) (3,102) (2,995) (16,743) (10,598) Operating non-interest expense (non-GAAP)i$ 270,082 $ 263,474 $ 268,363 $ 262,501 $ 276,918 Net income (GAAP)j$ 86,609 $ 143,269 $ 146,182 $ 120,144 $ 124,080 Provision for income taxes 37,238 49,076 50,068 40,944 44,987 Income before provision for income taxes 123,847 192,345 196,250 161,088 169,067 Provision for credit losses 27,403 28,199 28,769 31,820 17,136 Pre-provision net revenue (PPNR) (non-GAAP)k 151,250 220,544 225,019 192,908 186,203 Less: Non-interest income adjustmentsa (9,457) 5,532 (6,602) 9,739 3,882 Add: Non-interest expense adjustmentsb 70,040 3,102 2,995 16,743 10,598 Operating PPNR (non-GAAP)l$ 211,833 $ 229,178 $ 221,412 $ 219,390 $ 200,683 Net income (GAAP)j$ 86,609 $ 143,269 $ 146,182 $ 120,144 $ 124,080 Less: Non-interest income adjustmentsa (9,457) 5,532 (6,602) 9,739 3,882 Add: Non-interest expense adjustmentsb 70,040 3,102 2,995 16,743 10,598 Tax effect of adjustments (7,419) (2,158) 902 (6,621) (3,620) Operating net income (non-GAAP)m$ 139,773 $ 149,745 $ 143,477 $ 140,005 $ 134,940

38 Non-GAAP Reconciliation: Earnings Per-Share and Performance Metrics For the Quarter Ended ($ in thousands, except per-share data)3/31/202512/31/20249/30/20246/30/20243/31/2024 Select Per-Share & Performance Metrics Earnings per share - basicj/r$ 0.41 $ 0.69 $ 0.70 $ 0.58 $ 0.60 Earnings per share - dilutedj/s$ 0.41 $ 0.68 $ 0.70 $ 0.57 $ 0.59 (1) Efficiency ratioh/f6 9.06 %5 4.61 %5 4.56 %5 9.02 % 60.57 % Non-interest expense to average assetsh/n 2.68 %2 .06 %2 .08 %2 .16 % 2.22 % Return on average assetsj/n0 .68 %1 .10 %1 .12 %0 .93 %0 .96 % Return on average tangible assetsj/o0 .70 %1 .14 % 1.15 %0 .96 %0 .99 % PPNR return on average assetsk/n1 .19 %1 .70 %1 .72 % 1.49 %1 .44 % Return on average common equityj/p 6.73 %1 0.91 %1 1.36 %9 .85 % 10.01 % Return on average tangible common equityj/q9 .45 % 15.41 % 16.34 % 14.55 % 14.82 % Operating Per-Share & Performance Metrics Operating earnings per share - basicm/r$ 0.67 $ 0.72 $ 0.69 $ 0.67 $ 0.65 Operating earnings per share - dilutedm/s$ 0.67 $ 0.71 $ 0.69 $ 0.67 $ 0.65 (1) Operating efficiency ratio, as adjustedu/y5 5.11 %5 2.51 %5 3.89 %5 3.56 %5 6.97 % Operating non-interest expense to average assets i/n2 .13 %2 .03 % 2.05 %2 .03 % 2.14 % Operating return on average assetsm/n 1.10 %1 .15 %1 .10 % 1.08 %1 .04 % Operating return on average tangible assetsm/o1 .13 % 1.19 %1 .13 %1 .12 % 1.08 % Operating PPNR return on average assetsl/n 1.67 %1 .77 %1 .69 %1 .70 %1 .55 % Operating return on average common equitym/p 10.87 %1 1.40 %1 1.15 %1 1.47 %1 0.89 % Operating return on average tangible common equitym/q1 5.26 % 16.11 % 16.04 % 16.96 % 16.12 % (1)Tax-exempt income was adjusted to a taxable equivalent basis using a 21% tax rate and added to stated revenue for this calculation.

39 Non-GAAP Reconciliation: Operating Efficiency Ratio, as Adjusted For the Quarter Ended ($ in thousands)3/31/202512/31/20249/30/20246/30/20243/31/2024 Non-interest expense (GAAP)h $340,122 $266,576 $271,358 $279,244 $287,516 Less: Non-interest expense adjustmentsb (70,040) (3,102) (2,995) (16,743) (10,598) Operating non-interest expense (non-GAAP)i 270,082 263,474 268,363 262,501 276,918 Less: B&O taxest (3,150) (3,495) (3,248) (3,183) (3,223) Operating non-interest expense, excluding B&O taxes (non-GAAP)u $266,932 $259,979 $265,115 $259,318 $273,695 (1) Net interest income (tax equivalent)v $426,098 $438,424 $431,184 $428,434 $424,344 Non-interest income (GAAP)d 66,377 49,747 66,159 44,703 50,357 (1) Add: BOLI tax equivalent adjustmentw 1,362 1,390 1,248 1,291 1,809 Total Revenue, excluding BOLI tax equivalent adjustments (tax equivalent)x 493,837 489,561 498,591 474,428 476,510 Less: non-interest income adjustmentsa (9,457) 5,532 (6,602) 9,739 3,882 Total Adjusted operating revenue, excluding BOLI tax equivalent adjustments (tax equivalent) (non-GAAP)y $484,380 $495,093 $491,989 $484,167 $480,392 (1) Efficiency ratioh/f6 9.06 % 54.61 % 54.56 % 59.02 %6 0.57 % (1) Operating efficiency ratio, as adjusted (non-GAAP)u/y5 5.11 %5 2.51 %5 3.89 %5 3.56 % 56.97 % (1)Tax-exempt income was adjusted to a taxable equivalent basis using a 21% tax rate and added to stated revenue for this calculation.