Where is the deepest canyon in the United States?
Hells Canyon
The early miners were next to follow. In the 1860s gold was discovered in river bars near present-day Hells Canyon National Recreation Area, and miners soon penetrated Hells Canyon. Gold mining was not profitable here.  Evidence of their endeavors remains visible along the corridor of the Snake River.  Later efforts concentrated on hard-rock mining, requiring complex facilities.  Evidence of these developments is visible today, especially near the mouth of the Imnaha River.[5]