Which river forms much of the border between Idaho and Oregon and is known for Hells Canyon?

The Snake River forms a significant portion of the border between Idaho and Oregon and is historically known for its dramatic landscapes, including Hells Canyon, which is one of the deepest canyons in North America. The river flows through a range of terrains, offering unique geological features like steep cliffs and lush valleys. Hells Canyon, carved by the Snake River, provides a significant natural landmark and a popular area for outdoor recreation.

The Columbia River, while significant in the Pacific Northwest, primarily defines the border between Washington and Oregon rather than Idaho and Oregon. The Colorado River is mainly known for carving the Grand Canyon and is located in the southwestern United States, far from the northern borders of Idaho and Oregon. The Red River, on the other hand, flows in a completely different region and does not have any geographical relation to Idaho and Oregon. Therefore, the Snake River is the correct choice because of its geographical relevance and prominence in shaping the border between these two states along with its iconic feature, Hells Canyon.