ERS-1 radar images acquired 14 months apart studied by differential radar interferometry show the wide-area distribution of aseismic creep along the fault segment northwest of Parkfield, California. A sharp discontinuity in the interferometric phase of less than 2 cm equivalent line-of-sight displacement extends over 80 km in the differential interferogram, coincident with the mapped trace of the active San Andreas fault and consistent with the expected and measured fault motion. Although patterns of strain associated with the transition from locked to creeping are not clearly identifiable, a decrease in creep displacement from northwest to southeast along the fault is visible. The observations are in agreement with a model of elastic deformation constrained by in situ data that supports a maximum expected deformation signature of 10 mm across the image. ¿ 1998 American Geophysical Union