Streams on the east slope, having steeper gradients and therefore more rapid flow than the other streams, cut spectacular canyons on this side of the range. As these streams have worked back into the giant block, they have caused the divide to migrate westward, diverting more and more drainage to the east and leaving the great peaks standing like monuments on the ever-widening east slope.

East of the Teton Fault, in the Jackson Hole area, another great earth block lies deeply buried beneath debris brought down into the basin by mountain streams and glaciers. Changes wrought by the great glaciers of the Ice Age have given the region much of its distinctive character. Glacial erosion is strikingly evident in the sharply chiselled peaks, the U-shaped canyons and the profound basins (“cirques”) at their heads, and the numerous little alpine tarns (lakelets occupying ice-gouged basins). The irregular wooded ridges of Jackson Hole, on the other hand, are due to glacial deposition, being composed of bouldery debris heaped up by the ice. Some of these moraines form the dams which enclose the beautiful lakes at the foot of the Teton Range—Phelps, Taggart, Bradley, Jenny, Leigh, and Jackson Lakes. The broad terraced plains of Jackson Hole are for the most part great sheets of gravel spread out on the valley floor by the glacial streams of the Ice Age.

Small glaciers still found among the Teton Peaks are now believed to be youthful ice bodies only a few thousand years old, rather than the dwindling remnants of great glaciers of the Ice Age, as was formerly thought.

A fuller account of the geologic features is given on the reverse side of the topographic map of Grand Teton National Park, for sale at the museum.