Jackson Hole is a by 6- to 13-mile-wide (10 to 21 km) graben valley with an average elevation of , its lowest point is near the southern park boundary at . The valley sits east of the Teton Range and is vertically displaced downward , making the Teton Fault and its parallel twin on the east side of the valley normal faults with the Jackson Hole block being the hanging wall and the Teton Mountain block being the footwall. Grand Teton National Park contains the major part of both blocks. Erosion of the range provided sediment in the valley so the topographic relief is only . Jackson Hole is comparatively flat, with only a modest increase in altitude south to north; however, a few isolated buttes such as Blacktail Butte and hills including Signal Mountain dot the valley floor. In addition to a few outcroppings, the Snake River has eroded terraces into Jackson Hole. Southeast of Jackson Lake, glacial depressions known as kettles are numerous. The kettles were formed when ice situated under gravel outwash from ice sheets melted as the glaciers retreated.