Snake

Course

The Snake River starts to the north of Two Ocean Pass near the southern border of Yellowstone National Park, about 9,200 feet (2,800 m) above sea level in the Rocky Mountains of Wyoming. The river descends west through the high mountains of the Teton Wilderness meeting the Lewis River and continuing south into Jackson Lake in Grand Teton National Park, a natural glacial lake enlarged by Jackson Lake Dam. Joined by Pacific Creek and Buffalo Fork below the dam, it meanders southward through the alpine valley of Jackson Hole situated on the plain in front of the Teton Range to the west and the Gros Ventre Range to the east.

Below the town of Jackson it forms the Snake River Canyon of Wyoming, turns west and crosses into Idaho, where the Palisades Dam forms Palisades Reservoir.

History

Starting around the end of the last glacial period, the Snake River Plain was inhabited by hunter-gatherers of the ancient Clovis (10000–9000 BCE), Folsom (9000–8000 BCE) and Plano (8600–5800 BCE) cultures. Along the lower Snake River in Washington, the Marmes Rockshelter – flooded in 1968 after the construction of Lower Monumental Dam – has yielded archeological evidence of continuous human occupation from about 9000 BCE until about 1300 CE. Starting about 2200 BCE, people in the western Snake River basin began to adopt a semi-sedentary lifestyle, with an increased reliance on fish (primarily salmon) and food preservation and storage. Shoshoni-speaking peoples arrived in the Snake River Plain between 600 and 1500 CE.

Ecology and environmental issues

The World Wide Fund for Nature (WWF) divides the Snake River into two freshwater ecoregions – the Upper Snake and Columbia Unglaciated – with Shoshone Falls marking the boundary between the two. Shoshone Falls has presented a total barrier to the upstream movement of fish at least since the Bonneville flood 15,000 years ago. The Big Wood River (the main tributary of the Malad River) is also included in the Upper Snake ecoregion, due to the presence of a separate natural waterfall barrier. As a result, only 35 percent of the fish fauna above Shoshone falls, and 40 percent of the Big Wood River's fish fauna, are shared with the lower Snake River.

Geology

The present-day course of the Snake River was pieced together over millions of years from several formerly disconnected drainage systems. Much of what would become the Pacific Northwest lay under shallow seas until it was uplifted starting about 60 million years ago (Ma). The outlet of the ancestral Columbia River to the Pacific was established about 40 Ma. By about 17 Ma, the "Salmon-Clearwater River", or the modern day lower Snake River, flowed west into the Columbia and on to the Pacific. Another ancient river system drained what is now the western Snake River Plain.