Till, believed to be of pre-Wisconsin age, is widely distributed throughout the Rocky Mountains, in most places as small isolated patches. Some deposits lack morainal form and lie only on interstream divides; others, having a poorly preserved morainal form, overlap from the canyons onto the divides.

The deposits tend to be finer-grained, more compact, and more strongly jointed than younger Wisconsin deposits. Commonly they have a thick very strongly developed mature soil profile preserved on them.

In some places, the physical relations of the deposits to one intracanyon erosion surface and two precanyon erosion surfaces suggest that they represent three stages of glaciation. This suggestion is confirmed by stratigraphic evidence in the La Sal Mountains, Utah, and in Glacier National Park, Montana, where three tills, each capped by a thick and very strongly developed mature soil profile, are superposed.

The three stages may represent the Nebraskan, Kansan, and Illinoian stages of the Mississippi Valley, but no convincing evidence for such a correlation has been found.

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