The Guaymas Basin in the central Gulf of California is a young spreading center about 1.6-2.1 km deep, which is covered with a thick sequence of sediments. It provides an excellent location to investigate geothermal processes at a sedimented rift using conventional oceanographic heat-flow equipment. Rapid sediment accumulation at this site precludes the formation of "normal" oceanic crust by extrusion; instead, basaltic sills intrude semiconsolidated and unconsolidated sediments, expelling pore water and driving vigorous hydrothermal circulation. Deep-seated heat sources also drive longer-lived convection within and beneath the sediment cover.

The continuous sediment cover has allowed detailed and extensive mapping of the distribution of surface heat flow throughout the Guaymas Basin; more than 400 heat-flow measurements have been collected since 1959 in crust ranging in age from 0 to about 3 Ma. Away from the sites of crustal accretion, the background heat flow throughout the Guaymas Basin is about 180 ± 10 mW/m². Within the two spreading centers of the basin, known as the northern and southern troughs, heat-flow values range from 0 to nearly 9 W/m², and variations of two orders of magnitude occur over distances as short as a few hundred meters. Heat-flow patterns generally follow the northeast-southwest structural trend of the central troughs but are locally controlled by recent intrusive acti ity and associated hydrothermal circulation.

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