Mokelumne River

The Mokelumne River ( or ; ''Mokelumne'', Miwok for "People of the Fish Net") is a -long river in northern California in the United States. The river flows west from a rugged portion of the central Sierra Nevada into the Central Valley and ultimately the Sacramento–San Joaquin River Delta, where it empties into the San Joaquin River- Stockton Deepwater Shipping Channel. Together with its main tributary, the Cosumnes River, the Mokelumne drains in parts of five California counties. Measured to its farthest source at the head of the North Fork, the river stretches for .

The river is colloquially divided into the Upper Mokelumne River, which stretches from the headwaters to Pardee Reservoir in the Sierra foothills, and the Lower Mokelumne River, which refers to the portion of the river below Camanche Dam. In its lower course, the Mokelumne is used heavily for irrigation and also provides water for the east San Francisco Bay Area through the Mokelumne Aqueduct. Several major tributaries of the river have been developed for the generation of hydroelectric power.

The name is Plains Miwok and is constructed from ''moke'', meaning fishnet, and ''-umne'', a suffix meaning "people of".Bright, William (1998). ''1500 California Place Names: their origin and meaning''. University of California Press; Berkeley, California, 1998. . The town of Mokelumne Hill was named for the river in about 1850.

Course

The Mokelumne is formed by the confluence of several forks that rise in the central Sierra Nevada in the Stanislaus National Forest. The North Fork is the largest, originating at Highland Lakes at an elevation of . From its source it flows north then west for to Salt Springs Reservoir. Below Salt Springs it receives the Bear River from the north and then passes through the smaller Tiger Creek Reservoir before joining with the Middle Fork southeast of Pine Grove. The lower portion of the North Fork defines the border between Amador and Calaveras Counties.

The Middle Fork rises at on the west side of Bailey Ridge, near Ganns. It flows generally west, past Wilseyville and West Point, to its confluence with the North Fork. The South Fork begins at an elevation of very near the head of the Middle Fork, and flows west , roughly parallel and south of the Middle Fork, to join the Middle Fork about above the confluence of the North and Middle Forks.

The confluence of the North and Middle Forks forms the Mokelumne River proper. The main stem flows west-southwest past Mokelumne Hill into Pardee Reservoir, formed by the -high Pardee Dam. Below Pardee the river flows directly into Camanche Reservoir, formed by Camanche Dam. The entire stretch of the Mokelumne between the forks and a point just above Camanche Dam defines the Amador—Calaveras county line; below here, it flows westwards into San Joaquin County.

The Camanche Dam is the first non-passable barrier for anadromous fish. Below Camanche Dam the Mokelumne meanders to its confluence with the San Joaquin River, first continuing southwest out of the Sierra foothills past Lockeford and then turning northwest at Lodi, where the small Woodbridge Dam impounds the river, forming Lodi Lake. The river receives Dry Creek from the east near Thornton and shortly afterwards receives its major tributary, the Cosumnes River, from the northeast. At this point, the river has reached its northernmost point about south of Sacramento.

The river continues west then south into the Sacramento–San Joaquin River Delta where it becomes tidal and splits into a pair of distributaries, the North and South Mokelumne River (not to be confused with the North and South Forks in the Mokelumne headwaters) which together encircle the of Staten Island. About downstream the branches rejoin, and two miles (3.2 km) below this point the Mokelumne flows into the San Joaquin River.

Watershed

The Mokelumne River watershed drains in parts of Alpine, Amador, Calaveras, San Joaquin, and Sacramento Counties. Elevations range from sea level at the confluence with the San Joaquin River to at the crest of the Sierra Nevada in the headwaters of the North Fork.

The Mokelumne watershed divide borders the basins of the American River on the north, the Calaveras and Stanislaus rivers to the south, and the Carson River to the east. The American, Calaveras and Stanislaus rivers, like the Mokelumne, drain westwards into the Central Valley, while the Carson flows eastwards into the Great Basin. Drainage within the Mokelumne watershed generally occurs from east to west with all of the perennial streams originating in the Sierra Nevada.

The Mokelumne River and its headwater forks above Lodi drain the southernmost part of the basin. The part of the basin above Pardee Dam is referred to as the Upper Mokelumne River Basin and drains about , or 25.7% of the total watershed. The Cosumnes River and its own North, Middle and South forks drain about in the northern part of the basin, or about 33.8% of the total watershed. Dry Creek, which itself is formed by four Sierra streams – Jackson, Sutter, Amador and Rancheria Creeks – drains most of the area between the upper Mokelumne and Cosumnes basins, or about .

The upper watershed is situated principally in Alpine, Amador and Calaveras Counties and consists mostly of wilderness managed under various federal designations. Most of the Mokelumne and Cosumnes River headwaters lie within the Stanislaus and Eldorado National Forests. Much of the upper watershed is also protected under the Mokelumne Wilderness. The Salt Springs State Game Refuge is located along the Mokelumne River near Salt Springs Reservoir. There are also significant private holdings in the upper basin including commercial timber land and protected watershed areas administered by the East Bay Municipal Utility District, which diverts urban and industrial water from Pardee Reservoir.

The lower watershed, mainly within San Joaquin and Sacramento Counties, is part of the rich agricultural region of the Central Valley. Grapes are the major crop grown in the Mokelumne River watershed; as of 2001, vineyards comprised 51% of the basin's farmland. Of the remaining land, 31% is used for livestock, 9% for orchards, and 8% for annual crops. About in the lower basin are part of the Mokelumne River AVA.

In May 2021, it was reported that a trove of 5- to 10-million-year-old fossils was unearthed in June 2020 in the Mokelumne River watershed near Valley Springs, California, including a two-tusked mastodon, a four-tusked gomphothere, rhinoceros, camel, horse, tortoise, tapir, bird, fish, and other specimens.

History

The Mokelumne River basin was originally inhabited by Yokuts, Miwok, and Wintun

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