Between the park’s numerous mountain ranges, there are valleys, which are classified according to their method of formation. Queen Valley and Lost Horse Valley were formed by a difference in the rate of erosion between the rock underlying the valley itself and the rock composing the surrounding mountains. The mountainous rock is more resistant to erosion and therefore rises above the valleys. Pleasant Valley, on the other hand, was formed by down-dropped motion along faults that formed basins (called grabens). Some valleys have playas: lakes that may contain water a few weeks a year during the rainy season.