 Tuolumne and Merced River systems originate along the crest of the Sierra Nevada in the park and have carved river canyons 3 @,@ 000 to 4 @,@ 000 feet ( 910 to 1 @,@ 220 m ) deep . The Tuolumne River drains the entire northern portion of the park , an area of approximately 680 square miles ( 1 @,@ 800 km2 ) . The Merced River begins in the park 's southern peaks , primarily the Cathedral and Clark Ranges , and drains an area of approximately 511 square miles ( 1 @,@ 320 km2 ) . 
