The Jefferson River originates at the junction of the Big Hole and Beaverhead rivers, near Twin Bridges, Montana, and runs northeasterly 77 miles to Three Forks, where it joins the Madison and Gallatin rivers to form the Missouri River. In its upper reach, the Jefferson meanders widely through a grassy valley between the Continental Divide on the west and the Tobacco Root Mountains on the east. Near Whitehall, approximately halfway along its course, the Jefferson turns east away from the mountains. It cuts deeply through a high, semi-arid plain to flow past rocky cliffs, sagebrush, and native grasses. From its confluence with the Boulder River near Cardwell to Missouri Headwaters State Park, the Jefferson is primarily confined to a single channel, except near Three Forks. There it braids, forming many islands and side channels in a rich bottomland. The Jefferson River is extensively used as a source of irrigation water and is subject to severe dewatering in low-water years. The Ruby and Clark Canyon reservoirs, which impound major upstream tributaries of the Jefferson, affect the river's flow pattern. The river itself challenges floodplain developments with its natural tendency to migrate. In addition to fishing, the Jefferson River and its floodplain provide opportunities for waterfowl hunting, trapping, floating, sightseeing and asparagus picking.