Profile surveys in Snake River basin, Idaho
Snake River, the largest tributary of the Columbia, rises among the high peaks of the Rocky Mountains in Yellowstone National Park, heading in the divide from which streams flow northward and eastward into the Missouri, southward to the Colorado and the lakes of the Great Basin, and westward to the Columbia. From the headwater region, including Shoshone, Lewis, and Heart lakes, in Yellowstone National Park, the river flows southward, broadening into Jackson Lake (4 miles wide and 18 miles long) and passing through Jackson Valley (8 miles wide and 40 miles long), beyond which, near the Idaho-Wyoming line, it enters a long canyon. At the south edge of Madison County, Idaho, it receives Henrys Fork, below which the Snake flows southward and westward across Idaho to a point near Homedale, near the Oregon-Idaho line, where it turns abruptly northward and beyond which it forms for about 170 miles the boundary between Idaho and Oregon and for 30 miles more that between Idaho and Washington. It enters Washington at Lewiston, flows northwest, west, and southwest, and joins the Columbia near Pasco.