Walla Walla River
Overview
 
The Walla Walla River is a tributary of the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

, joining the Columbia just above Wallula Gap
Wallula Gap
Wallula Gap is a large water gap of the Columbia River through basalt anticlines in the Columbia River Basin in the U.S. state of Washington, just south of the confluence of the Walla Walla and Columbia rivers...

 in southeastern Washington in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The river flows through Umatilla County, Oregon
Umatilla County, Oregon
Umatilla County is a county located in the U.S. state of Oregon. It is included in the 8 county definition of Eastern Oregon. The county is named for the Umatilla River. In 2010, its population was 75,889...

 and Walla Walla County, Washington. Its drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 is 1758 square miles (4,553.2 km²) in area.
The headwaters of the Walla Walla River lie in the Blue Mountains
Blue Mountains (Oregon)
The Blue Mountains are a mountain range in the western United States, located largely in northeastern Oregon and stretching into southeastern Washington...

 of northeastern Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

.
 
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