Rocas Alijos lies 180 nautical miles west of Baja California. It comprises several exposed rocks that surmount a large oceanic volcano rising from the ocean floor well off the continental shelf. It is located at the transition zone between two major biologic provinces, at a latitude where the Pacific Current turns westward to form the north Pacific trans-oceanic current. In spite of its obvious importance for biogeographical studies, the remoteness of Rocas Alijos and its small size thwarted any major scientific work until very recently, and the topography, biota, and oceanographic conditions of the site remained largely unknown. During 1990, and again in 1993, Cordell Expeditions, a nonprofit research organization based in Walnut Creek, California, undertook expeditions to describe the site. A scientific team of 30 was onsite 31 October-7 November 1990, and a scientific team of 12 was onsite 10-15 February 1993. Since most of the Rocas Alijos site is subtidal, much of the examination and specimen collection was done by scuba, although several remote sampling techniques were also used. The exposed rocks were sampled by climbers, and megafauna were observed from shipboard.

Zusammenfassung
Rocas Alijos lies 180 nautical miles west of Baja California. In spite of its obvious importance for biogeographical studies, the remoteness of Rocas Alijos and its small size thwarted any major scientific work until very recently, and the topography, biota, and oceanographic conditions of the site remained largely unknown.

Inhalt
I Background.- Overview: The Cordell Expeditions to Rocas Alijos.- Discovery and Exploration of Rocas Alijos.- II Rocks.- The Geographic Position of Rocas Alijos.- Photogrammetry of the Emerged Rocks at Rocas Alijos.- Volcanic Rocks from Rocas Alijos.- III Water.- Bathymetry of Rocas Alijos.- Tidal Pattern at Rocas Alijos.- Ocean Currents at Rocas Alijos.- Vertical Water Temperature Profiles at Rocas Alijos.- Chemical Analysis of Seawater at Rocas Alijos.- IV Sediment and Soil.- Marine Sediment from Rocas Alijos.- Terrestrial Soil at Rocas Alijos.- V Microbiota.- Marine Bacteria of Rocas Alijos.- Foraminifera of Rocas.- Plankton from Rocas Alijos.- VI Mesobiota.- Marine Flora of Rocas Alijos.- Sponges from Rocas Alijos.- Hydroids from Rocas Alijos.- Stony Corals from Rocas Alijos.- Polychaetes from Rocas Alijos.- Isopods from Rocas Alijos.- Anthozoans, Bryozoans, Brachiopods, and Tunicates of Rocas Alijos.- Decapod Crustaceans and Pycnogonids of Rocas Alijos.- A New Species of Hippolytid Shrimp from Rocas Alijos.- Barnacles of Rocas Alijos.- Marine Mollusks of Rocas Alijos.- Echinodermata Collected at Rocas Alijos.- Terrestrial Invertebrates of Rocas Alijos.- VII Megabiota.- Fishes of Rocas Alijos.- Birds Observed at Rocas Alijos.- Avian Specimens from Rocas Alijos.- Marine Mammals of Rocas Alijos.- VIII Supplementary.- Onsite Observations at Rocas Alijos.- Weather and Sea Conditions at Rocas Alijos.- Comparison of the 1990 and 1993 Expeditions to Rocas Alijos.- IX Summaries.- Summary of Results.- Species List.- General Index.