The Walker Lane and northern part of the eastern California shear zone form a boundary zone accommodating differential motion between the Sierra Nevada and western Great Basin. Within the boundary zone, Global Positioning System velocities show a westward increase from 2–3 mm/yr in the central Great Basin to ∼14 mm/yr in the Sierra Nevada and a clockwise rotation from west-northwest to northwest. In the same region, incremental extensional strain axes recorded by earthquake focal mechanisms and fault-slip inversion show an east to west counterclockwise rotation of 50°, from parallel with the velocity field in the central Great Basin to nearly orthogonal to the velocity field along the eastern flank of the Sierra Nevada. Unlike plane-strain deformation within the central Great Basin, the progressive deviation between the orientation of extension axes and the velocity field in the boundary zone is a product of nonplane strain. The boundary zone records active constriction formed in conditions varying from wrench-dominated to extension-dominated transtension.