The San Juan Bautista (SJB) segment forms the northern transition zone of the creeping section of the San Andreas fault. It is an area of moderate seismicity; the largest instrumentally-recorded earthquakes have been M5.5. However, historic records suggest six M ≥ 6 earthquakes occurred near the SJB segment between 1840 and 1899. It is also an area that has experienced several slow earthquakes. We perform a joint inversion of GPS and InSAR data to determine the current rate and distribution of interseismic creep. We find two low-slip/locked segments at mid-seismogenic depths that may represent source regions for the 19th century earthquakes. We find that the SJB segment is currently accumulating strain energy at the rate of one M6.3--6.7 earthquake per century. At this rate, the 1840--1899 sequence released 135--510 years of accumulated moment deficit.