DISTRIBUTION OF PINEDALE/BULL LAKE GLACIERS IN IDAHO: INTERPRETATION OF 1:24,000 TOPOGRAPHIC MAPS

Modern large-scale maps with small contour intervals display topography in detail sufficient for geomorphic interpretation based on extensive field experience. In Idaho, 1:24,000 quadrangles clearly show land forms (cirques, U-shaped valleys, moraine ridges) indicative of the presence and extent of late Pleistocene alpine glaciers, although it is usually not possible to separate Pinedale from Bull Lake records without field inspection, especially since Pinedale ice generally, but not everywhere, extended beyond Bull lake limits. Glacier outlines can then be transferred to 1:250,000 map sheets in order to have a final compilation small enough to use conveniently. The result is a single composite map depicting essentially synchronous ice cover throughout Idaho during major portions of Pleistocene time, the closing phase of which overlapped the presence of humans in northwestern America. A brief glance at the compiled map shows that the percentage of area that was covered by alpine glaciers in Idaho was greater than that of any other state, not surprising in view of widespread mountainous terrain and relatively high latitude. Glacier distribution was strongly influenced by topographic details that provided snow catchment and shading. At times of maximun glacierization many cirques were completely filled so that ice was confluent between basins on opposites sides of high divides or flowed across a divide onto a mountain slope that had no cirque. Local ice carapaces and caps were therefore common.