Elevation changes derived from precise leveling surveys conducted by the National Geodetic Survey in 1931, 1941, 1972, and 1974 along two routes crossing the Imperial fault in southern California represent the first documented examples of spatially coherent vertical movements associated with strike-slip faulting in the United States. The leveling routes cross the northern section of the fault that broke at the time of the 1940, M7.1 Imperial Valley earthquake. The observed vertical movements, which extend approximately 25 km east and west of the fault, are among the largest observed anywhere in the United States. These movements are consistent with simple elastic models of coseismic and postseismic ''secondary vertical deformation due to right-lateral strike-slip movement along a finite length fault. The spatial and temporal patterns of deformation suggest a simple scenario consisting of large coseismic slip on the southern part of the Imperial fault which transferred stresses to the northern part of the Imperial fault and the Brawley fault (en echelon fault northeast of Imperial fault). These stresses were subsequently released primarily by aseismic creep. The estimates of coseismic faulting determined from the leveling observations are roughly consistent with field observations of horizontal surface offset made after the earthquake as well as with some estimates derived from triangulation measurements. The postseismic fault offsets reported here suggest slip to shallower levels than previous estimates of postseismic slip determined from repeated triangulation measurements. The overall shallow slip (coseismic plus postseismic) required by the leveling observations is larger on the southern part of the Imperial fault than on the northern part of this fault or on the Brawley fault. The 1979, M6.6 Imperial Valley earthquake apparently eliminated some of this difference in overall shallow slip by causing surface offsets on the northern part of the Imperial fault and the southern Brawley fault, even though the epicenter for the 1979 event was located on the southern Imperial fault. Other geophysical observations in this part of the Imperial Valley (fault creep, seismicity, seismic faulting) suggest that stick-slip on the southern part of the Imperial fault and creep on the nothern part of this fault and on the Brawley fault may characterize the long-term fault behavior in the Imperial Valley.