The Purisima Formation is the most common rock outcrop on the outer shelf and it forms ledges and hardgrounds for many benthic species that require a hard substrate. Outcrops on the outer shelf are most commonly the result of relatively more resistant cuestas of dipping rock strata that were probably eroded down to their present relief at times of lowered sea level, the last of which occurred prior to 15,000 years ago. Such sand troughs are most common in the offshore former Fort Ord area, and the deepest one occurs offshore of Seaside at a depth of 56 m. The seafloor imagery and interpreted geology will be published along with other studies of the seafloor and water-column in a special volume of the journal Marine Geology in summer or fall 1999. Measurements, plans, and results related to physical oceanography in the Sanctuary during 1998 have been many.
Measurements span the last two years and include near-bottom currents and sediment data.
During the first year, an additional mooring was deployed at a depth of about 60 m off Santa Cruz. Results also suggest that suspended sediment transport on the shelf is mainly storm-driven and that Monterey Bay is the origin of the suspended sediments. During this time, unusually strong poleward currents throughout the water column of up to 40 cm per second were observed, particularly at mid-water depths. The currents shifted abruptly equatorward in early 1998 at the outer-shelf mooring. Physical oceanographic conditions at the thermocline depths offshore returned to near normal by the time of the 1998 spring upwelling season.