More than a hundred earthquakes have been recorded in southern California during the period February-September, 1920. These earthquakes have originated along several different faults in the vicinity of Los Angeles, but all of them are believed to have resulted from the adjustment of stresses set up in the region by the same general tectonic movements. The series of shocks felt in Los Angeles on July 16th originated along faults which cut Miocene and Pliocene rocks in the northern part of the city. The three strongest shocks on July 16th had epicentral intensities of between VI and VII in the Rossi-Forel scale; and they were felt over areas of from 500 to 2500 square miles. The known seismic history of southern California and the magnitude of the post-Pleistocene movements both indicate that the seismicity of the region is relatively high. There are many faults in the vicinity of Los Angeles; some of which are known to be active, while others are suspected of being active. Fortunately those within the city are short, while the longer ones are seven to thirty miles away, and are therefore less dangerous in so far as Los Angeles is concerned.