A belt of arc-parallel, northeast vergent contractional deformation, the East Sierran thrust system (ESTS), crops out for ~150 km along the east side of the Sierran continental margin arc. The ESTS is nowhere wider than ~20 km, and it accommodated an estimated minimum of ~9.3 km of horizontal shortening. Remarkably, it experienced repeated episodes of broadly coaxial and coaxial-planar contractional deformation beginning prior to 188 Ma and continuing past 140 Ma. We postulate that the ESTS resulted primarily from episodic underthrusting of the back arc lithosphere beneath the east edge of the Sierran arc, facilitated by a buttressing effect of the arc. As a result of this process, rocks along the east flank of the batholith, including the ESTS, were episodically shortened against the arc buttress. The ESTS experienced significant deformation during the Nevadan orogeny, indicating that contractional to transpressive deformation affiliated with this event affected the eastern wall rocks of the arc as well as its western wall rocks.