Humboldt, river, c.300 mi (480 km) long, rising in several branches in the mountains of NE Nev. It meanders generally west to disappear in Humboldt Sink, W Nevada. Along with its tributaries, the Humboldt drains most of N Nevada. Its length varies with the season, and its volume decreases downstream. Most of the towns of N Nevada are located on the river in a valley used by a major highway and railway as an east-west route. Near Lovelock the Humboldt project of the U.S. Bureau of Reclamation is served by the Rye Patch Dam (completed 1936), which impounds water for irrigation. Forage crops are raised along the river. Known to early explorers and named by J. C. Frémont, the river was an important route followed by many of the emigrants from Salt Lake City to central California. Its course supplied wagon trains with water and grass.