Laminated, richly diatomaceous sediments in the central Gulf of California are confined to the slopes of the basins. An investigation has been made of the water, organisms, and sediments in the Guaymas and San Pedro Martir Basins, which are the sites of most abundant diatom accumulation. The laminated sediments in these basins occur where the basin floor intersects the oxygen minimum in the water column. Burrowing organisms do not occur in this poorly oxygenated zone, and the laminations remain undisturbed. Such organisms are present in deeper parts of the basin where oxygen concentrations are higher, and, through their digging activities, the sediments are homogenized. In contrast to previously described occurrences of laminated sediments, the laminated diatomaceous sedi ents of the Gulf of California occur on the slopes of a basin which has free communication at all depths with the open ocean.