Gravel benches above Lower Tangle Lake indicate that the lake was at one time about 50 feet higher than the current level. The land adjacent to the upper Delta River includes steep alluvial slopes, rock cliffs and spectacular geologic features. Plants Vegetation includes various plant associations ranging from arctic tundra to spruce-poplar forests. Grasses, sedges and forbes grow on the highest, most exposed slopes and above the brush line. Willows grow on moist, lowland sites and in the many brushy draws draining the side slopes.
Dwarf birch occupies the drier sites associated with well drained soils.
Alder is found on the steep slopes of hillsides and canyon walls. Forests of white and black spruce occur below an elevation of 3,200 feet in small pockets along the river and on some hillsides. Open spruce-poplar forests occupy lowland sites along the river and some midslopes of hillsides adjacent to the river. Understory plants are varied and abundant. Fireweed, bistort, rose, mountain-avens, burnet, and shrubby cinquefoil are just some of the many plants found in the area.