The absence of a major earthquake over the past 300 years along the southern San Andreas fault has prompted a large-scale effort toward understanding the nature of present-day loading and stress accumulation at the plate boundary. The growing archive of GPS data in California is beginning to provide a detailed synoptic picture of the accumulation of stress and strain along this zone. However, because typical earthquake cycles (~150 yrs) span time periods beyond those of GPS measurements (~15 yrs), sophisticated computational models are key for understanding the dynamics of the lithosphere and advancing our ability to forecast major ruptures. Using a 3D time-dependent model of the earthquake cycle, I simulate both plate boundary deformation and stress accumulation of the San Andreas Fault System due to historical earthquakes spanning the last 1000 years. Modeled deformation is constrained by geologic, geodetic, and paleoseismic data; modeled stress variations arise from changes in fault slip rate, fault geometry, and fault locking depth. Model estimates indicate that the San Andreas Fault System accumulates stress along different fault segments at a rate of 0.5 - 9 MPa/100yrs and that a significant level of accumulated stress (~7 MPa) is currently concentrated along the majority of the southern San Andreas fault, consistent with the absence of a major earthquake on this segment over the past 300 years. Elevated stress of this magnitude may have important implications for seismic hazard analyses given that modeled stress levels of the southern San Andreas appear to be approaching those of historically great earthquake events (7+ MPa).