Kinematic assumptions of geodetic inversions for fault slip require that the slip sums to the (plate) boundary velocity. This assumption neglects permanent off-fault deformation, which could account for discrepancies between geologic and geodetic estimates. We use three-dimensional mechanical models to assess if unaccounted permanent strain surrounding faults could contribute to slip rate discrepancies across disconnected faults within the Mojave Desert (California, USA) portion of the eastern California shear zone (ECSZ). We modified fault configurations derived from the Southern California Earthquake Center Community Fault Model to better represent the disconnected nature of active faults in the ECSZ south of the Garlock fault. The models with revised fault geometry produce slip rates that better match geologic strike-slip rates, thus validating the revisions. Within these models, off-fault deformation accounts for 40% ± 23% of the total strain across the ECSZ. This suggests that a significant portion of the discrepancy between the geologic and geodetically modeled slip rates in the ECSZ could be due to the geodetic inversion model assumption of zero permanent off-fault deformation.