 The 1979 Imperial Valley earthquake occurred at 16 : 16 Pacific Daylight Time ( 23 : 16 UTC ) on October 15 just south of the Mexico – United States border . It affected Imperial Valley in Southern California and Mexicali Valley in northern Baja California . The earthquake had a relatively shallow hypocenter and caused property damage in the United States estimated at $ 30 million USD . The irrigation systems in the Imperial Valley were badly affected , but no deaths occurred . It was the largest earthquake to occur in the contiguous United States since the 1971 San Fernando earthquake eight years earlier . 
