Shoshone Lake is a U.S. backcountry lake with an area of 8,050 acres with an elevation of 7,795 feet in the southwest section of Yellowstone National Park, Wyoming. It lies at the headwaters of the Lewis River, a tributary of the Snake River. The U.S. Fish and Wildlife Service believes that Shoshone Lake is the largest backcountry lake in the lower 48 st…Shoshone Lake is a U.S. backcountry lake with an area of 8,050 acres with an elevation of 7,795 feet in the southwest section of Yellowstone National Park, Wyoming. It lies at the headwaters of the Lewis River, a tributary of the Snake River. The U.S. Fish and Wildlife Service believes that Shoshone Lake is the largest backcountry lake in the lower 48 states that cannot be reached by a road. The Yellowstone Caldera is located within the lake.