The mean and seasonal circulation of the Gulf of California is simulated with a three-dimensional numerical model, forced by the Pacific Ocean through specifying the sea level, the temperature, and the salinity fields at its entrance. At the sea surface, the wind and the heat and freshwater fluxes are specified. The model reproduces the observed mean and seasonal variability of sea level, of heat and salt balances, and the sea surface temperature (SST) climatology. It also reproduces the general surface circulation of the northern gulf, which consists of a seasonally reversing basin-wide gyre. It is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the SST. Tides provide the mixing to upwell the cooler subsurface waters in the large islands area, and the heating from the surface raises the SST. The general circulation of the southern part of the gulf is due to the wind and the Pacific forcing. In the Ekman layer, two periods of anticyclonic circulation and one cyclonic per year occur; below this layer, two cyclonic periods develop. In the northern part, the tides play an important role in producing mean residual currents, and both, tides and winds, compete against the Pacific forcing to produce a cyclonic and anticyclonic circulation once a year. Contrary to conclusions of previous studies, the thermohaline circulation is found to be unimportant in the gulf.