Hells Canyon. The deepest canyon in North America. The canyon rims stand on average 4,000 to 5,000 feet above the Snake River and reaches a maximum of 8,000 feet above the river when measured from the highest peak of the Seven Devils Mountains in Idaho. Flowing south to north through the gorge, the Snake River drops from a little over 2,000 feet to 700 feet above sea level, a drop of approximately 1300 feet in 195 river miles. This represents a gradient of almost seven feet per mile, or slightly less than the gradient of the Colorado River through the mighty Grand Canyon.
Behind the spectacular scenery is an equally fascinating geologic history. Most of the rocks of Hells Canyon were formed far from their present position, far to the west in the ancient Pacific Ocean. The rocks tell the story. Fossil corals found in limestone were formed in tropical latitudes over 210 million years ago. Other rocks were laid down on the flanks of ancient volcanoes rising above the ocean. Carried piggy-back via plate tectonics, these rocks were scraped off on the western margin of North America at a time when dinosaurs still roamed the earth. In only the last few millions of years these rocks have been also uplifted, eroded and dissected by rivers to create this spectacular and incredibly rugged landscape.
In spite of the challenging environment, some species, such as the Rocky Mountain bighorn sheep, manage to thrive. The original population of bighorns was wiped out earlier this century by diseases caught from domestic sheep. Recent efforts have been successful in reintroducing bighorns to their ancestral home, providing us with exciting up-close encounters along the river.
