History

The geologic history of the rocks of Hells Canyon began 300 million years ago with an arc of volcanoes that emerged from the waters of the Pacific Ocean. Over millions of years, the volcanoes subsided and limestone built up on the underwater platforms. Between 130 and 17 million years ago, the ocean plate carrying the volcanoes collided, and became part of the North American continent. A period of volcanic activity followed, and much of the area was covered with floods of basalt lava, which smoothed the topography into a high plateau. The Snake River began carving Hells Canyon out of the plateau about 6 million years ago. Significant canyon-shaping events occurred as recently as 15,000 years ago during a massive outburst flood from Glacial Lake Bonneville in Utah.

The earliest known settlers in Hells Canyon were the Nez Percé tribe. Others tribes visiting the area were the Shoshone-Bannock, Northern Paiute, and Cayuse Indians. The mild winters, and ample plant and wildlife attracted human habitation.

Humans have historically used Hells Canyon Wilderness for farming, ranching and mining activities. Sheep and cattle have grazed this area of Northeastern Oregon since the 1730s, as the Nez  Percé grazed horses and cattle in the main canyons. By the 1800s, homesteaders on the Oregon benchland were grazing sheep, cattle, and horses throughout the valley and canyons. Cattle grazing continues today in a small portion of the Wilderness, as permitted in the 1964 Wilderness Act, which allows some traditional activities to continue as long as wilderness values are not compromised. Some mining has also occurred, primarily on the Idaho side of the Wilderness.

In 1806, three members of the Lewis and Clark Expedition entered the Hells Canyon region along the Salmon River. They turned back without seeing the deep parts of the canyon. It was not until 1811 that the Wilson Price Hunt expedition explored Hells Canyon while seeking a shortcut to the Columbia River. Hunger and cold forced them to turn back, as did many explorers who were defeated by the canyon's inaccessibility. There remains no evidence in the canyon of their attempts; their expedition journals are the only documentation.