Between 1924 and 1928 the canyon was the site of the St. Francis Dam . At 11:57 PM on March 12 , 1928 , the dam catastrophically failed , and the resulting flood took the lives of as many as 400 people . 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
1906 San Francisco earthquake
1906 San Francisco earthquake
San Francisquito Canyon