Subsurface investigation of the Imperial fault zone approximately 50--60 m south of the U.S.-Mexico International Border in Mexicali Valley reveals that only the 1940 Imperial Valley earthquake (ML 7.1) has produced significant surface slip in the past 300 years. The 1940 earthquake produced about 5 m of slip in this vicinity, as indicated by an offset tree line. We excavated a buried channel adjacent to these trees and determined that it is also offset 5 m. These data indicate that at least the upper meter of sediments has only been displaced by the 1940 event. One other slip event of undetermined magnitude is recorded within the lacustrine highstand deposits of the last lake about 300 years ago. There is no evidence of earlier faulting events in sediments that possibly may correlate to the penultimate lake approximately 550 years B.P. Below an unconformity, ~4000-year-old deltaic deposits are intensely faulted by previous slip along the Imperial fault. These data suggest that the slip rate on the Imperial fault for the past 300--550 years is only about 15--20 mm/yr, substantially less than that expected from geodetic measurements and regional structural models. This in turn suggests that either slip is accommodated by other faults in the border region or that strain release on the Imperial fault is characterized by episodic (clustered) behavior. ¿ American Geophysical Union 1996