Two overflows, originating at sills in the northern Gulf of California, are marked by strong average downstream slopes of 17 and 4%. Near‐bottom stratification upstream of both sills is relatively strong, but the near‐bottom water is very well mixed downstream of the sills. The homogenization of a thick bottom layer downstream, albeit close to the sills, is indicative of very strong mixing. Waters in the downstream basins are well ventilated with relatively high oxygen concentrations. These hydrographic patterns were observed during three different seasons. Time series of temperature, salinity, and potential density show that water, flowing over the sills, is essentially subsurface, subtropical water from the Pacific Ocean. The time series also indicate that water is nearly always denser at the sills compared to water in the downstream basins, despite the two‐fold (∼800 m) and more than three‐fold (∼1500 m) increase in depth. The long‐term (more than a year) average current at both sills is bottom intensified with maximum average speeds of 33 and 17 cm/s. There are also strong tidal currents at the sills, although the subinertial currents near the bottom are quite persistent with nearly no flow reversals. Transports, estimated exclusively with the mean flow, are about 0.08 and 0.09 Sv (1 Sv = 1× 106, m3/s), which agree well with previous estimates based on shorter time series and a lower vertical resolution. These results indicate that the deep water at both downstream basins are renewed by these overflows, which enter at sill depths ≤400 m and are capable of reaching the deepest part of both basins. The overflows appear to be responsible for the main mechanisms that transform subsurface, subtropical water into Gulf of California water.