Hells Gate lies on river bottom left over from the great ice age floods about 15,000 years ago. At the south end of the park are basaltic columns from the Pomona flows 14 million years ago. Hells Gate State Park was once the site of a Nez Perce Village. Little is left of the village, but depressions south of the campground are the remnants of pit houses used for years by the Nez Perce as they fished for lamprey near Astoin Creek.
