Settlements of considerable size were established in very rough country along the upper San Gabriel River . Prospect Bar , located up the narrow canyon of the East Fork , grew to include " a boarding house , two or three stores , blacksmith shop , butcher shop , etc. " A flood in November 1859 destroyed the settlement , but four months later it was re-established as the town of Eldoradoville , near the junction of the East Fork and Cattle Canyon . The period from 1859 to 1862 was the most prosperous of the San Gabriel gold rush ; Wells Fargo stages alone shipped some $ 15,000 ( $ in dollars ) worth of gold per month out of Los Angeles County , most of it from the San Gabriel diggings . John Robb , who ran a saloon in Eldoradoville , claimed he " made more money by running the sawdust from the floor of the Union Saloon through his sluice box than he was able to make from real mining , so prodigal and careless of their pokes were the miners and gamblers of those days . " By 1861 , Eldoradoville had an estimated population of 1,500 . The town prospered until the Great Flood of 1862 , the largest in California 's recorded history , swept the canyon clean : Mining on the San Gabriel did continue after the flood of 1862 , but never on the same scale as before . A second wave of gold seeking began in the early 1930s along the East Fork . A September 1932 '' Los Angeles Times '' article described it as a " leisurely gold rush " and reported : Several gold mining camps sprang up along the East Fork , the largest including the Upper and Lower Klondike . Mining during the 1930s focused on finding the finer particles and dust left behind from the previous gold boom . For many it was a source of income during the Great Depression , and for some others was a recreational activity . These mining camps were again obliterated , along with much else along the San Gabriel River , during the great flood of 1938
Great Flood of 1862
Great Flood of 1862
San Gabriel River (California)