 The geology of the Yosemite area is characterized by granitic rocks and remnants of older rock . About 10 million years ago , the Sierra Nevada was uplifted and then tilted to form its relatively gentle western slopes and the more dramatic eastern slopes . The uplift increased the steepness of stream and river beds , resulting in formation of deep , narrow canyons . About 1 million years ago , snow and ice accumulated , forming glaciers at the higher alpine meadows that moved down the river valleys . Ice thickness in Yosemite Valley may have reached 4 @,@ 000 feet ( 1 @,@ 200 m ) during the early glacial episode . The downslope movement of the ice masses cut and sculpted the U @-@ shaped valley that attracts so many visitors to its scenic vistas today . 
