Comparison of preearthquake vertical geodetic surveys with postearthquake surveys in the region affected by the magnitude 5.7 Oroville earthquake of August 1, 1975, indicates appreciable elevation changes. The data are consistent with 0.36 m of normal slip on a 12¿10 km2 rectangular fault dipping 60¿ to the west. Comparison of level surveys run 1 and 6 months after the earthquake suggests an additional 0.08 m of postseismic slip on the fault. Horizontal geodetic data do not show any significant changes, but the horizontal data are noisier than the vertical data and allow as much as 0.7 m of coseismic left lateral slip within a 95% confidence limit. There is no evidence for postearthquake dilatancy recovery, but the data are not adequate to exclude small amounts (10 mm) of relaxation, or even larger amounts if the dilatant region were very broad (80 km in diameter).