This volume covers Leg 63 of the cruises of the Drilling Vessel Glomar Challenger. Leg 63 of the International Phase of Ocean Drilling began on 9 October 1978 when the Glomar Challenger left Los Angeles harbor and ended on 26 November in Mazatlan, Mexico. This cruise was the first investigation of the region off southern California and Baja California by the Deep Sea Drilling Project. Eleven holes at seven sites were drilled. In the North Pacific, the southward-flowing California Current is a major eastern boundary current that has dominated the hydrography off southern California and Baja California since the Cretaceous. Changes in the configuration and intensity of this current throughout the Neogene apparently are reflected in variations in the marine biota locked in sediments of that age. A primary objective of Leg 63 was to investigate the fluctuations of this eastern boundary current along a north-south transect. This information would also aid in biostratigraphically correlating open-ocean planktonic zones with local California zonations. Spanning the last 30 m.y., the complicated tectonic history of the continental margin off California and Baja California comprises changes from a subduction zone to a transform boundary and then to an inactive margin. A second objective of Leg 63 was to define and clarify this history using information on sedimentation, unconformities, basement ages, and paleomagnetic reconstructions gained from drilling, in conjunction with geophysical data and pre-existing bottom samples. At several sites we expected to recover Miocene sediments rich in organic matter. A third objective of Leg 63 drilling was to investigate the degree and mode of diagenesis of this organic matter under conditions of shallow burial and low temperature. This information would be useful in evaluating diagenetic pathways of organic matter in similar sediments and sedimentary rocks that are important hydrocarbon sources onshore.