Five years of measurements from the Global Positioning System (GPS) satellites collected between 1986 and 1991 are used to investigate deformation in the offshore regions of southern California. GPS provides the first practical technique to make precise geodetic measurements in the region. The geodetic network is situated along the California coastline from Vandenberg (120.6¿W, 34.6¿N) to San Diego, with additional sites on Santa Cruz, San Nicolas, Santa Catalina, Santa Rosa, and San Clemente Islands. The precision of horizontal interstation vectors is subcentimeter, and the interstation vector rate between OVRO and Vandenberg agrees with the very long baseline interferometry derived rate to within one standard deviation. No significant motion is observed in the western Santa Barbara Channel between Vandenberg and Santa Rosa Island, 0.5¿1.6 mm/yr, where the quoted uncertainties are one standard deviation. Motions in the eastern Santa Barbara Channel are consistent with compressional deformation of 6¿1 mm/yr at N16¿3¿E. This motion is in agreement with seismicity and an independent geodetic analysis for the period 1971--1987 (Larsen, 1991). San Clemente Island is moving relative to San Diego at the rate of 5.9¿1.8 mm/yr at a direction of N38¿20¿W. The motion between San Nicolas Island and San Clemente Island, 0.8¿1.5 mm/yr, is insignificant. ¿ American Geophysical Union 1993