A large aureole of grooved terrain surrounds Olympus Mons, a Martian shield volcano. Curvilinear scarps which face away from and gentle interior slopes which face toward the volcano characterize this terrain. It is concentrated on the downslope side of Olympus Mons and rises as an uplift above the surrounding plain. Previous work attributed grooved terrain either to Olympus Mons volcanism, or to erosion of prior volcanoes in this area, or to magmatic crustal doming, unroofed by later erosion. These are not believed correct. The grooved terrain is probably large-scale gravity thrust sheets. The load of the Olympus Mons shield on a thick sequence of frozen bedded volcanic and aeolian type sediments caused thrusting. Movement was probably near the base of the Martian permafrost, where internal heat melted the ice, a process creating a natural zone of yield. Models of the situation may improve the present estimate of water in the Martian regolith.