Between 1924 and 1926, the canyon was the site of the construction of the St. Francis Dam. The Los Angeles Department of Water and Power began filling a reservoir in the San Francisquito Canyon in 1926. At 11:57pm on March 12, 1928, the dam catastrophically failed, and the resulting flood took the lives of at least 431 people.[2][3] The collapse of the St. Francis Dam is considered to be one of the worst American civil engineering disasters of the 20th century and remains the second-greatest loss of life in California's history, after the 1906 San Francisco earthquake and fire. The ruins of this disaster can still be seen today.
Since 1820, San Francisquito Canyon and San Francisquito Pass were part of the original route of the El Camino Viejo, an alternate land route to the El Camino Real for reaching northern Spanish and Mexican colonial Alta California. From 1854, the wagon route of the Stockton - Los Angeles Road followed its course as did the Butterfield Overland Mail in California from 1858 to 1861. This Tejon Pass Route and the Tehachapi or Midway Route (first followed by the Southern Pacific Railroad), remained the major north–south wagon and later automobile routes to the San Joaquin Valley until the construction of the more direct Ridge Route in 1915.[4]
Today, a two-lane road named after the canyon itself connects Santa Clarita to the mountain communities of Green Valley and Elizabeth Lake. It roughly parallels the river's course between San Francisquito Pass and its southern terminus in the northern Santa Clarita Valley.
