<PAGE>

                                  Exhibit 13.1

COLUMBIA BANCORP 2005 ANNUAL REPORT

Celebrating the Corps of Discovery

Columbia Bancorp is the financial holding company for Columbia River Bank, which
provides services primarily to non-metropolitan areas throughout the Pacific
Northwest. The Bank operates 20 branches located in communities typically
comprising less than 250,000 in population. In addition to a full array of
banking services and products, Columbia River Bank also provides
mortgage-lending services through CRB Mortgage Team and brokerage services
through CRB Financial Services Team.

We have two stories to tell you. One deals with our 2005 annual report,
presented inside. The other story honors Lewis and Clark. We at Columbia River
Bank are proud to be part of this bicentennial celebration, and to be serving
much of the surrounding territory passed through by the Corps of Discovery 200
years ago.

We are an independent community bank, driven by the core values of integrity,
excellence, commitment, and teamwork.

Our particular focus in 2005 has been on a word that CEO Roger Christensen uses
often around the bank:

"BALANCE"

It is clear to all of us that achieving a balance between the needs of our
employees, customers, and shareholders helps to put Columbia River Bank on a
solid, progressive footing for the future, even in a highly competitive
environment or in unpredictable economic times.

It's a win-win-win approach, to be further examined in the pages that follow.

As the Bank continues to grow and industry technology advances, our need for
bright and energetic employees increases.

How do people feel about working for our Bank?

Let's begin with a statistic that tells a lot: more than 50 percent of our
employees have been with us at least five years even taking into account new
hires and retirees.

In truth, Columbia River Bank is a great place in which to work. And that is not
just the CRB management team saying so. For the second year in a row, based on
employee surveys taken by Oregon Business, our bank was ranked among "100 Best
Companies to Work For in Oregon."

Hiring and retaining good people is always a major focus for us, especially in
the

                                     Page 1
<PAGE>

current growth curve. Our commitment is to create a work environment that
empowers employees to do their best. We go far in providing the support and
compensation necessary for each person to achieve the highest level of personal
performance, which in turn brings about opportunities for advancement.

Above all, CRB is a place where people can freely express ideas. In this open
atmosphere, employees can be credited for many positive changes occurring at the
bank. They have helped to make us a better organization -- for our customers,
our shareholders, and themselves.

Providing advanced bank products to our customers is expected; where we "go
beyond" is contributing to the communities we serve. A snapshot of staff
activities:

Last September, Kaye Stephenson, Operations Officer for the White Salmon branch
of Columbia River Bank, worked the White Salmon Huckleberry Fest Pie Booth along
with employees Lyn Mittag and Linda Creager.

For every fundraiser like this in our market area, there is undoubtedly a CRB
person involved. The same holds true for organizations like Rotary, Kiwanis, and
Chamber of Commerce, as well as scouts, churches, schools, sports teams, health
care organizations, -- the list goes on. That is because all of us, from branch
to branch, believe that helping the community in which we live and operate goes
right along with the banking side of things.

At our Meadow Springs Branch in Richland, Washington, Liz Torres serves as
secretary for HAAP (Hispanic Academic Achievers); Bill McKay is a Scouts Merit
Badge Counselor, Julie Killian is vice chair of the Lourdes Health Network; and
Jerry Ball participates in BOMA (Building Owners and Management Association).

In Central Oregon, ten team members participate in 29 community organizations.
Here is a glimpse: Tom Van Hemelryck, United Way; Shelle Pack, March of Dimes
Walk; Jan Weiss, new OSU Alumni Association in Central Oregon; Kim Luckman,
Central Oregon Visitors Association; Joanne Luke, Women's Resource Center;
Kristee Chick, Network of Entrepreneurial Woman; Nancy Paskewich, SMART program;
Robert Killen, Regional Arts Council; Nancy O'Connor, Bend Vision Committee; and
Terri Ramsdorph, Rotary.

At our Newberg Branch, Ron Wolfe is active in organizations that really make a
difference, like Habitat for Humanity and Friendsview Retirement Center. Bob
Ficker, at the same branch, is board president of Providence Newberg Health
Foundation.

Many others at CRB -- like Mark Mascall at our Pendleton Branch, who is board
member of the NW Intercollegiate Rodeo Finals, and Tami Sampson, who puts in
time with the Pilot Rock Booster Club -- are supporting their communities in
capacities far too numerous to mention in one annual report.

Many thanks go to all these people for bringing truth to the phrase: "community
bank."

                                     Page 2
<PAGE>

Questions asked by institutional investors during quarterly teleconferences and
answers provided by Columbia River Bank executives.

Q: Could you comment on what you're seeing in the different markets in terms of
deposit pricing pressure and expectations going forward?

A: Shane Correa. We're seeing deposit pricing pressure primarily in Central
Oregon, and a little in the Tri-Cities area. But again, we've been able to hold
our own by competing on the basis of service, so we're real comfortable with our
market position and our ability to grow deposits.

Q: You've talked about technology systems. Are you doing major upgrades across
the platform and, if so, does this factor in as an expense drag later in the
year?

A: Roger Christensen. This is an ongoing process, and last year we hired
additional technology staff to integrate components we already purchased. There
will be some increase in expenses due to our investment in personnel and system
upgrades; however, our focus now will be to learn and apply the technology we
already have in place.

Q: It looks like mortgage banking revenues are up sequentially and the mid-part
of the year is typically the strongest for originations as far as purchased
homes. What's the outlook?

A: Craig Ortega. We feel positive about the mortgage segment for two reasons:
first, we're situated in good real estate markets and, second, along with
economic growth comes real estate construction. We've been successful with
originating construction loans and converting them into permanent mortgages.

Q: Based on your comments regarding the sale of loans as a capital management
and balance strategy, are you implying that loan growth could potentially
outstrip capital?

A: Greg Spear. No. The idea is to manage the balance sheet to ensure sufficient
regulatory capital. Historically, we rebuild capital in the fourth quarter and
first quarter, and I want to make certain that we have that same seasonal
strategy going into 2006. We're optimistic about the growth potential in all of
our markets. So we're not at risk, but I always like to be prudent and cautious
to ensure a strong regulatory capital position.

Interested investors may obtain copies of current Columbia Bancorp
teleconference scripts by e-mailing investorrelations@columbiariverbank.com.

                                     Page 3
<PAGE>

For Lewis and Clark, and Columbia Bancorp as well, success rides on choosing the
best people, planning meticulously, and equipping for all contingencies.

To our Shareholders, Customers and Friends:

I recently completed the book "Undaunted Courage," which chronicles the Lewis
and Clark expedition. I found many parallels between the management of their
westward trek and our successful management of Columbia Bancorp. These
forward-looking adventurers were extremely particular when assembling the team
that would accompany them. Both men scrutinized each individual joining the
expedition, with the goal of bringing only the best people on their
history-making journey.

Meriwether Lewis spent almost two years mentally preparing for the effort by
voraciously reading, seeking out experts, and trying to mitigate potential
pitfalls prior to the trip. He collected his data, tucked away his alternatives,
planned the travel route, and executed the plan.

As the journey was underway Lewis and Clark adhered to their plan, and when
circumstances voided that plan they used their wits and problem-solving
strengths to accomplish the task at hand.

At Columbia Bancorp and Columbia River Bank, we have embarked on our own
financial journey -- and we, too, hire only the best people to join us. Our goal
is to remain ranked as one of Oregon's Top 100 Employers by providing a work
environment that encourages creativity and the free expression of new ideas. We
provide our people the vision, the tools, and the training necessary to
reinforce our position as the bank that exceeds our shareholders, customers and
employees' expectations.

In 2005, Columbia Bancorp continued its pursuit of excellence in all areas of
performance. Our commitment to our customers and the communities we serve is
reflected by the introduction of new products -- such as free online bill payer,
shareholder checking, combined checking and savings -- and by the upgrade of our
Internet banking website.

Despite the string of devastating natural disasters that had the potential to
severely handicap the U.S. economy, Columbia Bancorp experienced a banner year.
A rebounding Northwest economy helped, but primarily it was an accomplishment
inspired by our dedicated staff throughout all of our branches and the loyalty
of our customers.

Balance sheet growth remains strong, with total year-end assets at $841.2
million, an 18% increase over the prior year. Our ROE for 2005 was 19.01%, which
placed us among the top 20% of all publicly traded banks with assets between
$500 million and $1 billion, according to SNL Datasource. In addition, we
achieved a return on assets of 1.77%, a 17% increase in deposits over 2004 to
$707.8 million, and $13.7 million in net income, or $1.36 per diluted share.

                                     Page 4
<PAGE>

Our commitment to continued enhancement of our product line and dedication to
the communities we serve is the impetus behind our goal of opening several new
branches in high-growth areas each year. To that end, we completed our Meadow
Springs branch in Richland, Washington, replacing our temporary branch in
Kennewick, Washington. Also in 2005 we broke ground for our new Pasco,
Washington branch and our Cherry Heights branch in The Dalles, Oregon. These
branches are scheduled to open during the first quarter of 2006.

We are excited by the opportunities presented to us by the new economic vitality
and steady growth in our market areas --Columbia River Gorge, Columbia Basin,
Willamette Valley, and Oregon High Desert.

Looking ahead, we will continue to create new products and services that meet
and exceed the business and personal needs of our customers, to grow the
Columbia Bancorp infrastructure, to remain at the forefront of new technology
and Internet banking, and to provide our investors a favorable return on equity.

From our management team, our loyal staff, and your Board of Directors, we thank
you for allowing us to serve you now and in the coming profitable years.

Roger L. Christensen
President and Chief Executive Officer

Richard E. Betz
Chairman of the Board

Columbia Bancorp board represents a broad spectrum of experience and strong
steering for our management and operations.

Columbia Bancorp and Columbia River Bank Executives and Senior Vice Presidents

Executives:

Roger L. Christensen
President and CEO, Columbia Bancorp and Columbia River Bank

James C. McCall
Executive Vice President, Chief Administrative Officer, Columbia River Bank

Craig J. Ortega
Executive Vice President, Chief Operating Officer, Columbia River Bank

Greg B. Spear
Executive Vice President, Chief Financial Officer,
Columbia Bancorp and Columbia River Bank

Britt W. Thomas
Executive Vice President, Chief Credit Officer, Columbia River Bank

R. Shane Correa

                                     Page 5
<PAGE>

Executive Vice President, Chief Banking Officer, Columbia River Bank

Senior Vice Presidents:

J. Michael  Anderson
High Desert Region

Robert V. Card
Audit Manager

Shawn P. Carroll
Gorge Region Manager

Staci L. Coburn
Controller

Robert J. Ficker
Willamette Valley Region Manager

Charla L. Fraley
Human Resource Director

Julie A. Killian
Business Banking Team Leader

A.J. Tarnasky
Credit Administrator

Todd M. Vallie
Director of Retail Banking

Thomas S. Van Hemelyryck
Business Banking Team Leader

M. Neil Zick
Senior Operations Officer

Columbia Bancorp Board of Directors
Charles F. Beardsley
Hershner & Bell
Real Estate & Insurance Sales & Brokerage
Owner

Richard E. Betz
Royal Columbia Farms, Inc.
Bud-Rich Potato, Inc.
Owner

William A. Booth
Booth & Kelly
Real Estate & Insurance
Owner

Lori R. Boyd
Boyd & Boyd, LLP
Co-Owner

Dennis L. Carver
Goldendale Chiropractic Clinic
Chiropractor/Owner

Roger L. Christensen
Columbia Bancorp

                                     Page 6
<PAGE>

President & CEO

Terry L. Cochran
Banker
Retired

James J. Doran
Jim Doran Chevrolet
Jim Doran Dodge Chrysler
Owner

Jean S. McKinney
McKinney Ranch
Owner

Donald T. Mitchell
Lumber Broker
Retired

Columbia River Bank branches are to be found in all reaches of the Lewis and
Clark territory.

GORGE REGION

Shawn P. Carroll
Senior Vice President and Manager
The Dalles Branch

Barry W. Smith
Vice President and Manager
White Salmon Branch

Nancy L. Johnson
Vice President and Manager
Goldendale Branch

John B. Kasberger
Vice President and Manager
Hood River Branch

Sandra K. Olson
Vice President and Manager
Westside Branch

HIGH DESERT REGION

James T. Booth
Assistant Vice President and Manager
South Redmond Branch

A. J. Losoya
Assistant Vice President and Manager
Wall Street Branch

Peter R. McCabe
Vice President and Manager
Madras Branch

Steven K. Tippett
Vice President and Manager
Redmond Branch

                                     Page 7
<PAGE>

M. Kim Luckman
Assistant Vice President and Manager
Bend Branch

J. Michael Anderson
Senior Vice President and Manager
Shevlin Branch

COLUMBIA BASIN REGION

Bryan A. Brock
Vice President and Manager
Hermiston Branch

Mark S. Mascall
Vice President and Manager
Pendleton Branch

Jim Hui
Vice President and Manager
Meadow Springs Branch

WILLAMETTE VALLEY REGION

Robert J. Ficker
Senior Vice President and Manager
Newberg Branch

Brad E. Lunt
Vice President and Manager
McMinnville Branch

Gary K. Gray
Vice President and Manager
Canby Branch

Independent evaluations of Columbia River Bank made in media, professional, and
financial circles.

Oregon Business Magazine's "100 Best Companies to Work for in 2005." Criteria:
attraction, retention and compensation, work environment, decision-making and
trust, management performance, career development and learning, and employee
benefits.

Independent Banker Magazine's "Top 20 ROA Community Banks," June 2005 issue.

Seattle Times' "Top Northwest 100 stocks," ranked 54th, in June 2005. To
qualify, companies must excel over a two-year span on four performance
measurements: return on equity, stock-price appreciation, sales per employee,
and operating income.

US Banker Magazine's "Top 200 Publicly Traded Community Banks," ranked 12th.
Based on 3-year average ROE, median EPS growth, average total risk, and price
performance.

The Oregonian's "Top 50 public companies," August 2005. Rank moved from 36 to
31.

Corporate and Shareholder
Information

Annual Meeting
The annual meeting of shareholders is scheduled for

                                     Page 8
<PAGE>

6:30 pm, Pacific Time, April 27, 2006, at Columbia Gorge Discovery Center, 5000
Discovery Drive, The Dalles, Oregon.

Financial Information
Columbia Bancorp news and financial results are available through our Web site
and by mail. For information about Columbia Bancorp, including news and
financial results and online annual reports, access our home page on the
Internet at ww.columbiabancorp.com.

At your request, we will mail to you our quarterly earnings news releases,
quarterly financial data reported on Form 10-Q and additional copies of our
annual reports, please contact:

Investor Relations
PO Box 1050
The Dalles, Oregon 97058
541-298-3191

Transfer Agent
Shareholder Services
Wells Fargo Shareowners Services
PO Box 64854
St. Paul, Minnesota 55164-0854
1-800-468-9716

Outside Legal Counsel

Marcus Williams
Davis Wright Tremaine
2600 Century Square
1501 Fourth Avenue
Seattle, WA   98101

Bennett H. Goldstein
Attorney at Law
1132 SW 19th Ave, Unit 106
Portland, OR   97205-1742

Independent Auditors

Moss Adams LLP
222 SW Columbia, Suite 400
Portland, Oregon 97201
Member FDIC

These financial statements have not been reviewed, or confirmed for accuracy or
relevance by the Federal Deposit Insurance Corporation.

                                     Page 9