A 500-pound, manganese-covered dolomite boulder was recovered from the ocean bottom near the continental slope off southern California, at 33 degrees 44'N latitude 120 degrees 45'W longitude. The dolomite has a massive appearance although a few barely discernible planar features may be bedding. Perfect dolomite rhombs are intergrown in a matrix of anhedral quartz with minor amounts of zeolites and detrital minerals. Characteristically, each dolomite rhomb has an inclusion at its center, which are similar to those in the cement of a dolomitic sandstone at Point Fermin, California. The dolomite may be a less-clastic, more calcareous facies of the Point Fermin dolomitic sandstone. Alternatively, it may be a dolomitized foraminiferal ooze. In which case it could be a fragment of a lithified deep-sea ooze, possibly part of seismic layer two.