Mokelumne History
Introduction
The
Mokelumne River was known to the early Spanish explorers as Rio de la Pasion. The vast
majority of early diaries and logs (1780s -1840s) suggest that the lower forks of the
Wakalumitoh, later Moquelumne, and ultimately, Mokelumne River were surrounded by immense areas of tule and marshes
that were evidently subject to annual flooding.
According to Edwin Bryant (1846), an officer who served under the command of John Charles Fremont, the great 19th century explorer known as the 'Pathfinder', "At a distance, the tule of these marshes presents the appearance of immense fields of ripened corn. The marshes are nearly dry (September-October) and to shorten our journey we crossed several of them without difficulty." The tule swamps and prairies were extensively used by livestock - sheep, mules, wild horses, and hogs - particularly during droughts when no other pasture was available. This significantly altered the appearance of the plains and tule swamps at a very early date. John Bidwell, one of the first settlers in the Sacramento Valley, noted a great change in the appearance of the plains from 1841 to 1843 due to horses, cattle, and sheep (Rogers 1891).
Early settlers used the Mokelumne River during the second half of the 19th Century for mining, hydropower development, and steamboat transportation. The most notable effect on the river, however, resulted from mining activity following the discovery of gold in 1848 and copper in 1861.
By 1850 so much water was diverted for gold mining that the riverbed was periodically left dry. Gold production peaked in 1854 and declined steadily until the turn of the century. Copper was discovered in 1861 along the Mokelumne River at Penn Mine, 68 miles upstream from the river mouth. Penn Mine was mined intensively between 1899 and 1919 and closed in 1919, but was later reopened and operated intermittently between 1937 and 1956. Mining techniques and the lack of restrictions on waste disposal often resulted in lethal heavy metal concentrations in the river. Mine effluent discharged to the river eliminated all downstream aquatic life, including salmon runs, in 1943 and 1944.
Hydroelectric Energy, Fisheries
Hydroelectric energy, developed by the predecessors of the Pacific Gas and Electric Company, was exported from the Mokelumne River basin to the San Francisco East Bay Area beginning in 1902. In 1929, water itself reached the East Bay Area when EBMUD completed Pardee Dam and the 82-mile long Mokelumne Aqueduct. With completion of EBMUD’s Camanche Reservoir Project (downstream of Pardee) in the late-1960s, EBMUD turned its attention to fishery issues in the lower Mokelumne River. EBMUD built a hatchery immediately downstream of Camanche which the California Department of Fish and Game operates.
Chinook salmon returns to the Mokelumne River, an indicator of the ecological health of the river ecosystem, were non-existent in some years as a result of mining activity and waste pollution. After cessation of active mining in the 1940s, salmon returns increased, only to decline to about 400 fish during the 1976-77 and 1987-92 droughts. Flow and non-flow ecosystem restoration efforts begun in 1992 by EBMUD, the California Department of Fish and Game, the U.S. Fish and Wildlife Service, Woodbridge Irrigation District, and other interested stakeholders have improved the fishery habitat. Salmon returns over the past five years have greatly exceeded the 3,812 fish long-term annual average.