A layer of turbidites roughly 600 m thick buries basement across the full width of the rift valley in the study area. The sediment section is disrupted by numerous normal faults and volcanic intrusions. Displacements on individual faults have been accumulating at rates of up to 15 mm/yr. The valley floor appears to be subsiding in most areas, at rates of up to 20 mm/yr. The sedimentation rate during the late Pleistocene is calculated to be in excess of 25 mm/yr. Heat flow in the valley is regionally low and relatively constant, averaging about 0.2 W/m2, as are temperatures predicted for the sediment-basement interface. Some variability is associated with disrupted zones in the inner rift. The highest heat-flow values are near the centers of intrusive volcanism. -from Authors