Measurements made during 1997--1998 in the northern Gulf of California show a persistent current flowing close to the bottom over a sill located at a depth of 340 m. The current flows at an average speed of 27 cm/s, 17 m above the bottom, toward the head of the gulf (NW). The sill is located near the Baja California coast and connects a relatively shallow basin (440 m) to the SE with a deeper one (800 m) to the NW. The current was recorded from November to August, and an estimate of the mean transport from November to March gives about 0.1 Sv (1 Sv = 106 m3 s-1). An independent transport estimation based on the salinity budget gave essentially the same value. A lower bound for the residence time of the water in the northernmost gulf is estimated to be 1.5 years. At depths above 260 m, mean currents were much more variable and weaker, but they veered abruptly toward the NW closer to the bottom. Another mooring, placed over the shallower continental shelf (100 m deep) on the mainland side, recorded weak mean currents toward the head of the gulf. Low-frequency current fluctuations show significant correlation between both sides of the gulf. During the 9-month observation period, the deep current fluctuations over the sill are in opposition to the currents over the shelf, which is consistent with a compensating mechanism for the exchange. Nearby coastal bottom pressure (CBP) is correlated with current fluctuations at both sides of the gulf, as well as with remote sea level at Manzanillo, well outside of the gulf. This latter correlation could be related to the El Ni¿o signal penetrating to the northern gulf. Correlation between CBP and currents on the Baja California side is consistent with a barotropic, geostrophic response. Around 200 m, the temperature increases from November to January, and this warming event is accompained with an increase in salinity. These features are consistent with an event of water mass formation in the northern gulf. Near-bottom currents and temperature are highly correlated, such that an increasing inflow is associated with cooler waters. The bottom current plays an important role in the exchange of the northern gulf with the Pacific Ocean.