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~ III G Hydraulic mining caused severe soil erosion. Miners tried to hold back the sediment with debris dams, but they often bmke and the sediment washed dow1lstream. 4 ^' f,_jti"~ . jJA~,~,"" "" ~~,-.., ...."1: "'>I ' J' California was a very different place in 1848, when the Gold Rush touched off a human migration that transformed its landscape and watersheds. Indigenous Native American tribes made up most of the population, along with a few scattered settle- ments of European immigrants, Although both Native Americans and European immigrants practiced subsistence agriculture, constructed modest irriga- tion systems and occasionally burned marshlands and grasslands to drive game, their activities had little or no effect on California's environment. The defining aquatic feature of that environment was the Delta formed by the Sacramento and San Joaquin rivers, two large river systems that drained the huge Central Valtey Basin into San Francisco Bay, In 1850, about 87 percent of the marshy Delta (320,000 acres) consisted of intertidal wetlands, areas that were alternately submerged and exposed THE GOLD RUSH The Gold Rush quickened the pace ot environ- mental change as miners flocked to streams and rivers in hopes of duplicating James Marshall's gold find in the American River, From simple panning and sluicing techniques, they soon developed more efficient methods such as hydraulic mining and dredging, Until it was outlawed in 1884 by the California Supreme Court's landmark Sawyer decision, hydraulic mining redirected natural water flows to powerful water cannons used to blast loose hillside soils and expose gold-bearing rock underneath. The practice caused severe soil erosion, clogging many streams with sediment ~'IliI by action of the tides and seasonal water flows, Plentiful water, combined with a mild Mediterranean climate, created a rich diversity of vegetation that supported large populations of animals ranging from tiny plankton to huge grizzly bears. Early visitors to the Central Valley reported its skies sometimes be- came black with migratory birds using the Pacific Flyway between Canada and South America, The Spanish explorers Pedro Fages and Father Juan Crespi described fhe Central Valley in 1772 as "a great inland lake that stretched farther than the eye could see, abounding with game, tish and fowl of all kinds." Sixty years later, John A. Sutter established a trading post at Sacramento and started several local industries, including the sawmill on the South Fork of the American River, where a gold nugget found In 1848 started the Gold Rush that transformed California. and choking the meandering water channels in the Delfa. Dredging continued well into the 20th Century, Dredges scooped up rock and soiltrom the river bed, separated the ore-bearing rock, then deposited the waste materials (called tailings) in piles alongside the dredge, Today, these tailings piles can still be seen for miles along rivers such as the American and Merced. All of the mining techniques had consequences for the streams and rivers. Dams dried up stream beds.