Global Positioning System (GPS) data collected in southern California from 1986 to 1989 indicate considerable strain accumulation across the Imperial Valley. Displacements are computed at 29 stations in and near the valley from 1986 to 1988, and at 11 sites from 1988 to 1989. The earlier measurements indicate 5.9¿1.0 cm/yr right-lateral differential velocity across the valley, although the data are heavily influenced by the 1987 Superstition Hills earthquake sequence. The 1988--1989 GPS displacements are best modeled by 5.2¿0.9 cm/yr of valley crossing deformation, but rates calculated from 15 years of terrestrial geodetic measurements (3.7¿0.1 cm/yr) fit the data nearly as well. The relatively high GPS rates are suspect because some measurements, especially the east-trending displacements, have large errors. There is evidence from GPS and very long baseline interferometry observations that the present strain rate along the southern San Andreas fault is smaller than the long-term geologic estimate, suggesting a lower earthquake potential than is currently assumed. Correspondingly, a higher earthquake potential is suggested for the San Jacinto fault. ¿ American Geophysical Union 1992