Figure 6-69 Ancient Oceans and Lakes on Mars (a) This Mars Global Surveyor image of a portion of Valles Marineris reveals terrain with “stair-step layers.” Such terrain is likely to have been created by sedimentation at the bottom of an ancient body of water. (b) This image of Burns Cliff, photographed by the rover Opportunity, shows a close-up of layers of rock laid down on a body of water on Mars that went through wet and dry periods.