North–south-striking and west-dipping Basin and Range province normal faults form the western edge of the Sierra Madre Occidental plateau in northeastern Sonora. These faults and associated half-grabens extend over a distance of more than 300 km between the San Bernardino basin in the north and the Sahuaripa basin in the south. An earthquake in 1887 ruptured three neighboring segments of this major fault zone. Our field mapping in this region indicates that the surface rupture of the 1887 earthquake extends farther to the south and is considerably longer (101.4 km end-to-end length) than previously reported.