Champlain Valley southward into the Valley of Vermont. The Vermont Lowlands are primarily underlain by sedimentary rocks, especially limestone and shale, though metamorphic rocks such as marble and slate are also present. Lake Champlain is situated in the Champlain Valley between the Green Mountains of Vermont and the Adirondack Mountains of New York, drained northward by the Richelieu River into the St. Lawrence River at Sorel-Tracy, Quebec (northeast of Montreal). Major tributaries of Lake Champlain include Otter Creek and the Winooski, Missisquoi, and Lamoille rivers in Vermont, and the Ausable, Chazy, Boquet, and Saranac rivers in New York. Lake Champlain also receives
Avalanche Lake (New York) miles to the east. Avalanche Lake feeds Lake Colden to the south, in the Hudson River watershed. To the north, the trail to the lake from the Adirondak Loj surmounts Avalanche Pass, which is only slightly above lake level but separates it from the Lake Champlain (St. Lawrence River) watershed. Following the lake toward Lake Colden, the trail is choked with large boulders, and a number of wooden ladders have been built to make passage possible. There are also three places where the trail takes to wooden catwalks, first built in the 1920s, that are bolted directly into the cliff