John Day River - Drainage Basin

Drainage Basin

Through its tributaries, the river drains much of the western side of the Blue Mountains, flowing across the sparsely populated arid part of the state east of the Cascade Range in a northwest zigzag, then entering the Columbia upstream from the Columbia River Gorge. It flows through exceptionally scenic canyons in its upper course, with several significant paleontological sites along its banks.

The main branch of the John Day River rises in the Strawberry Mountains in eastern Grant County. The North Fork heads on the western slope of the Elkhorn Mountains in northeastern Grant County. The Middlefork rises near Blue Mountain summit on the eastern edge of Grant County. The South Fork's source is in northern Harney County (about ten miles south of the Grant County line). The main, south and middle forks each have their heads in different parts of the Malheur National Forest, while the North Fork's source is located within in the Wallowa-Whitman National Forest. The main fork flows initially north, then west through the John Day Valley and through the cities of Prairie City, John Day and Mount Vernon. At Dayville, in western Grant County, it is joined from the south by the South Fork John Day River, then flows north through Picture Gorge and the Sheep Rock Unit of the John Day Fossil Beds National Monument.

At Kimberly in northwestern Grant County, it is joined from the east by the North Fork John Day River (which had already joined with the Middle Fork John Day River above Monument, Grant County, Oregon). The river then flows west across Wheeler County. At the county line with Jefferson County it flows north, past the Clarno Unit of the John Day Fossil Beds National Monument. As it approaches the Columbia River in north-central Oregon it flows in an increasingly meandering course, forming the boundary between Sherman County to the west and Gilliam County to the east.

The John Day River joins the Columbia from the southeast approximately 16 miles (26 km) northeast of Biggs. The mouth of the river is on the narrow Lake Umatilla reservoir, formed on the Columbia by the John Day Dam, approximately 2 miles (3.2 km) downstream from the mouth of the John Day.