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Columbia River is north of Oregon. - Lea
the Umatilla river
The Willamette River is the longest river "in" the State of Oregon. The Columbia and Snake are both much longer but are not completely "in" the State of Oregon.
The Grammart river flows north, and it is in Oregon.
Washington and Oregon border the Columbia River.
Denver is west of the Mississippi River, and Chicago is east of the Mississippi.
The Columbia River separates Washington State and Oregon.
If you mean Oregon and Washington, you'd be looking for the Columbia River...
Columbia River, Oregon.
The Sandy river and the Columbia river in Oregon
Denver is west of the Mississippi.
Denver is located in the South Platte River Valley on the High Plains.