Kammala jumla mai zuwa: Taron 1971 shi ne na farko a cikin jerin (1987 Whittier Narrows, 1991 Sierra Madre,
1994 Northridge) na girgizar ƙasa mai lalacewa wanda ya faru a kan kuskuren baya a yankin Los Angeles. Abubuwan da suka faru sun haifar da tattaunawa game da girgizar ƙasa mafi girma da za a iya samarwa ta ɗayan ɓarna, musamman a cikin Transverse Ranges, amma mahimmin mahimmancin ƙididdigar haɗarin girgizar ƙasa a California galibi shine San Andreas Fault da sauran ɓarnar da ke da alaƙa. Kodayake akwai rashin bayanan paleoseismic game da kuskuren baya a yankin Los Angeles, wani rami na rami a wani wuri a kan Sierra Madre-Cucamonga Fault ya bayyana cewa manyan girgizar asa biyu na tarihi sun faru a cikin shekaru 15,000 da suka gabata.