American River, in N. central California, is formed by the union of its N. and S. forks near the W. boundary of El Dorado county, 30 miles above Sacramento city, flows S. W. between the counties of Placer and Sacramento, and falls into Sacramento river near that city. The N. fork, considered by some as the true American river, rises among the hills at the base of the Sierra Nevada, and flows W. S. W., forming the boundaries between Placer and El Dorado counties for 100 miles. The S. fork flows from Bonpland lake through El Dorado county, and forms part of the division between the counties of Sacramento and El Dorado. These streams pass through one of the principal gold-mining districts.