For the ski area, see Mammoth Mountain Ski Area. Mammoth Mountain is a lava dome complex west of the town of Mammoth Lakes, California, in the Inyo National Forest of Madera and Mono Counties.It is home to a large ski area on the Mono County side. Mammoth Mountain was formed in a series of eruptions that ended 57,000 years ago.ammoth Mountain is home to the Mammoth Mountain Ski Area, founded by Dave McCoy in 1953. Mammoth is the highest ski resort in California and is notable for the unusually large amount of snowfall it receives compared to other Eastern Sierra peaks—about 400 annually—due to its location in a low gap in the Sierra crest.