Tuolumne River, CA

The Tuolumne River  in the U.S. state of California flows nearly 150 miles (240 km) from the central Sierra Nevada into the San Joaquin River in the Central Valley. Beginning at almost 13,000 feet (4,000 m) in elevation in Yosemite National Park, the river flows west through deep canyons before spilling into the foothills of the Sierra Nevada and being impounded in Don Pedro Reservoir. From Don Pedro Lake, the river flows through farmland in the Central Valley before finally terminating near Modesto. The San Joaquin then flows about 70 miles (110 km) further to its mouth in the Sacramento-San Joaquin Delta.

Slightly larger than its counterpart in the south, the Merced River, the Tuolumne River's upper watershed was shaped by glaciations in the previous Ice Age, which produced Hetch Hetchy Valley and the Grand Canyon of the Tuolumne. The river has been a source of controversy for many years, especially from Hetch Hetchy Valley. Much of its water is now diverted to San Francisco from Hetch Hetchy Reservoir, which fills the valley in the Sierra Nevada once compared to famous Yosemite Valley. More water is diverted from Don Pedro Lake to irrigate farmland in the Central Valley, which leaves the lower course of the river almost dry. Despite these extensive water system developments, the Tuolumne is still a popular area in Yosemite National Park, although far less visited than the Merced River.