At 6:00 a.m. on February 9, 1971, a magnitude 6.6 earthquake - the first large quake in the Los Angeles area in nearly 38 years -- shook the Southland, and was centered in the San Gabriel Mountains north of Sylmar.
Sixty four people lost their lives in the temblor, the first significant quake since the 6.4 Long Beach Earthquake in 1933, which set the standard for seismic codes for every building built after it. But the damage from the Sylmar quake, generally located in the San Fernando Valley, exceeded the tolerances of the Long Beach quake's codes, caused some $553 million in damage to buildings and infrastructure.
The Olive View Hospital in Sylmar, built on loose alluvial rock just below the San Gabriel Mountains, suffered severe tilting, fallen sections, and partial collapse. Three people were killed in the hospital, which was later demolished and rebuilt. A Veteran's Administration hospital also in Sylmar was partially destroyed. Freeway overpasses crumbled and collapsed in the Newhall Pass north of Sylmar. Portions of the Van Norman Dam west of Sylmar, which receives water from the Los Angeles Aqueduct, were destroyed, and residents were evacuated for fear of flooding, which was eventually averted. Outside of the San Fernando Valley, a number of structures, such as a number of Los Angeles Unified School District campuses, suffered damage considerable enough that school buildings spent the next several years in repair, or were replaced outright.
The Sylmar Earthquake caused existing seismic safety codes to be upgraded, and enabled the state legislature to pass the Alquist Hospital Seismic Safety Act in 1973.