<P> Prehistoric Native Americans lived along the Snake starting more than 11,000 years ago . Salmon from the Pacific Ocean spawned by the millions in the river, and were a vital resource for people living on the Snake downstream of Shoshone Falls . By the time Lewis and Clark explored the area, the Nez Perce and Shoshone were the dominant Native American groups in the region . Later explorers and fur trappers further changed and used the resources of the Snake River basin . At one point, a hand sign made by the Shoshones representing fish was misinterpreted to represent a snake, giving the Snake River its name . </P> <P> By the middle 19th century, the Oregon Trail had become well established, bringing numerous settlers to the Snake River region . Steamboats and railroads moved agricultural products and minerals along the river throughout the 19th and early 20th centuries . Starting in the 1890s, fifteen major dams have been built on the Snake River to generate hydroelectricity, enhance navigation, and provide irrigation water . However, these dams blocked salmon migration above Hells Canyon and have led to water quality and environmental issues in certain parts of the river . The removal of several dams on the lower Snake River has been proposed, in order to restore some of the river's once - tremendous salmon runs . </P> <P> Formed by the confluence of three tiny streams on the southwest flank of Two Oceans Plateau in Yellowstone National Park, western Wyoming, the Snake starts out flowing west and south into Jackson Lake . Its first 50 miles (80 km) run through Jackson Hole, a wide valley between the Teton Range and the Gros Ventre Range . Below the tourist town of Jackson, the river turns west and flows through Snake River Canyon, cutting through the Snake River Range and into eastern Idaho . It receives the Hoback and Greys Rivers before entering Palisades Reservoir, where the Salt River joins at the mouth of Star Valley . Below Palisades Dam, the Snake River flows through the Snake River Plain, a vast arid physiographic province extending through southern Idaho south - west of the Rocky Mountains and underlain by the Snake River Aquifer, one of the most productive aquifers in the United States . </P> <P> Southwest of Rexburg, Idaho, the Snake is joined from the north by Henrys Fork . The Henrys Fork is sometimes called the North Fork of the Snake River, with the main Snake above their confluence known as the "South Fork". From there it turns south, flowing through downtown Idaho Falls, then past the Fort Hall Indian Reservation and into American Falls Reservoir, where it is joined by the Portneuf River . The Portneuf River Valley is an overflow channel that in the last glacial period carried floodwaters from pluvial Lake Bonneville into the Snake River, significantly altering the landscape of the Snake River Plain through massive erosion . From there the Snake resumes its journey west, entering the Snake River Canyon of Idaho . It is interrupted by several major cataracts, the largest being 212 - foot (65 m) Shoshone Falls, which historically marked the upriver limit of migrating salmon . A short distance downstream it passes under the Perrine Bridge . Near Twin Falls, the Snake approaches the southernmost point in its entire course, after which it starts to flow west - northwest . </P>

Where is the mouth of the snake river