Resource assessments are essential, yet many are based on hydrodynamic models forced with coarse global data products for bathymetry and openboundary forcing. The aim of this paper is to examine how selection of: (1) two open source bathymetry products (GEBCO and ETOPO) and the inclusion of a higher-resolution bathymetry survey; and (2) considering different numbers of tidal constituents; affects the quantification of the tidal-stream energy resource for the Gulf of California. For the location with fastest current speeds, a 18 km wide passage between the San Lorenzo and San Esteban Islands, (herein San Lorenzo Passage), the annual mean power was estimated at around 120 MW and 20 MW when using freely available bathymetry data (GEBCO and ETOPO respectively), but increased to ~200 MW when using a bespoke dataset that was a combination of GEBCO and higher resolution bathymetry. Integrating higher resolution of bathymetry data within the model simulations increase the accuracy to resolve flows within the midriff region. We also compared the estimated energy computed using 29 tidal constituents compared with simulations that included just the M2 and S2 tidal constituents. The annual mean kinetic power density decreased by almost 1/3rd in the channel between San Lorenzo and San Esteban Islands, when considering just the M2 and S2 constituents, suggesting that diurnal and higher order harmonic constituents are important for accurate resource assessments in this region.