The Santa Barbara Channel is an elongated basin ~100 km by 40 km lying between the California coast, where it trends westward from greater Los Angeles to Pt. Conception, and the east-west trending Channel Island chain of four offshore islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa) ~50 km offshore (Fig. 1). A 500-m deep basin occupies the western center of the channel, and narrow continental shelves with depths the order of 100 m border its northern and southern boundaries. The channel is separated from the Southern California Bight to the east by a sill ~200 m deep between Anacapa and Port Hueneme. A sill ~400 m deep between Pt. Conception and San Miguel Island separates the channel from the open ocean to the west. The Santa Maria Basin is around the corner, north of Pt. Arguello. The surface waters of the channel are primarily mixtures of warm and saline waters from the Southern California Bight with colder and fresher waters upwelled near and poleward of Pts. Conception and Arguello. The California current flows equatorward past the western mouth of the channel, but its greatest speeds and most pronounced water properties (higher temperatures and lower salinities than those of the upwelled water) are usually found several hundred kilometers to the west of the channel. Prevailing winds around Pt. Arguello are equatorward, strong and steady in the summer, weaker but far more variable in the winter. The channel itself is a relatively sheltered region. The transition from sheltered to exposed wind conditions occurs over a few kilometers in the western channel. These conditions all make the circulation in the channel and adjoining regions more complex—and less well understood—than anywhere else along the west coast of the United States.