Geophysical images and structural cross sections of accretionary wedges are usually aligned orthogonal to the subduction trench axis. These sections often reveal underplated duplexes of subducted oceanic sediment and igneous crust that record trench-normal shortening and wedge thickening facilitated by down-stepping of the décollement. However, this approach may underrecognize trench-parallel strain and the effects of faulting associated with flexure of the downgoing plate. New mapping of a recently exposed transect across a portion of the Marin Headlands terrane, California, United States, documents evidence for structural complexity over short spatio-temporal scales within an underplated system. We documented the geometry, kinematics,...