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.
