Hodographs of resultant winds obtained from surface and upper-air observations at 21 stations in central California for the month of July 1958 are presented, together with trajectories of air parcels which pass into the Central Valley via the Bay area. A comparison of these observations with the results of current theories of the sea breeze indicates that local topography (not in the theory) is most important to air flow in the Bay area. Computed pressure differences between stations and the hodographs reveal that air in the Central Valley oscillates in phase with that new the coast, with the diurnal circulation most well developed below 1000-m elevation. Trajectories constructed with the aid of the surface hodographs indicate that air which enters the Central Valley by way of the Bay area tends to be diverted both northward and southward into the valley in the mean state. The nonlinear effects of velocity advection are of importance to the flow in the southern end of the valley.