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Mammoth Lakes Basin, California

The Mammoth Lakes Basin is a large glacial cirque basin that was carved by the grinding movement of glacial ice and rocks entrained within the ice.

Mammoth Lakes Basin including the treekill area next to Horseshoe L...
The gray area along the edge of Horesehoe Lake (lower right) is one of several areas around Mammoth Mountain where trees were killed recently by high concentrations of carbon dioxide gas in the soil. Mary Lake (left of center) is the 2nd largest in the basin. The largest lake, Duck Lake, is accessible only by foot and is hidden from view.(Credit: Brantley, S. R.. Public domain.)

The lakes in the lower basin, including Lake Mary, Lake George, and Horseshoe Lake, fill depressions in glacial moraine deposits. The lakes in the upper basin, including Duck Lake, Shelton Lakes, and Deer Lakes, fill depressions in the underlying bedrock (metamorphosed sedimentary rocks) that were scooped out by glaciers.