On May 3, 1887, a major earthquake shook much of the southwest United States and Mexico, an area of nearly two million square kilometers (Figure 1). This seismic event, with an estimated magnitude of 7.2 (DuBois and Sbar, in press), caused 51 deaths in northern Sonora, and major destruction of property in southeast Arizona, as well as adjacent portions of Mexico. Moderate damage also occurred in New Mexico. The 1887 epicenter was south of the Arizona-Mexico border in the San Bernardino Valley along the western front of the Sierra Madres Mountains (Figure 1). The northern end of the fault scarp formed during this earthquake is located only eight kilometers south of the present town site of Douglas, Arizona. The fault extends over 50 kilometers southward, with an average observed vertical displacement of three meters. In terms of magnitude, surface faulting and damage, the Sonoran earthquake ranks among the largest seismic events on record in the western United States, exclusive of California. Historically, it is the largest earthquake known to have caused damage in Arizona.
DuBois, S.M. and Smith, A.W., 1980, The 1887 Earthquake in San Bernardino Valley, Sonora: Historic accounts and intensity patterns in Arizona. Arizona Bureau of Geology and Mineral Technology, Special Paper #3, 108 p. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1578