Outwash plains are the deposits formed by streams which, during the Ice Age, issued from the glaciers. Of this origin are the broad, cobble-strewn flats, usually overgrown with sage, which cover the floor of Jackson Hole. They are diversified by bars, abandoned stream channels, terraces and "pitted plains", features of exceptional interest to one who examines them in detail. Several isolated buttes—Signal, Blacktail, and the Gros Ventre Buttes—rise like islands a thousand feet or more above these flats.
PROFILE OF THE YELLOWSTONE-GRAND TETON REGION
Each canyon gives evidence of the vigor with which the glacier it once contained gouged out its channel. In many places the rock of the broad floors and steep sides is still remarkably polished. Every canyon leads up to one or more amphitheaters, or cirques, with sheer bare walls hundreds of feet high. Tracing these ice-gouged canyons headward one will discover many rock-rimmed lakelets, some hung on precipitous mountain sides where one might be pardoned for asserting that no lake could possibly exist.
A CREVASSE IN TETON GLACIER
Crandall photo.