Argyre Planitia—A large impact basin (50°S, 318°E) in the southern highlands. Several channels enter the basin, suggesting that it may have once contained a lake. Numerous esker-like ridges (former sites of subglacial channels) on the floor of the basin support the supposition that a lake was formerly present that froze.
Ceraunius Tholus—A 100-km-diameter, 6-km-high volcano (24°N, 263°E) in Tharsis. The dense channeling on its flanks has variously been attributed to ash flows, rainfall, and melting of snow. A large channel that starts at the summit and leaves a delta at its terminus may have resulted from melting of snow in the summit crater by volcanic heat.
Cerberus Fossae—NNW-SSE trending graben (10°N, 157°E) to the southeast of Elysium. The graben has been the source of floods of both water and lava. Crater dating suggests that some floods may be as young as 10 million years before the present. Water from the graben may have pooled in the Cerberus plains to the southeast of the graben.
Chryse Basin—A low area (20°N, 320°E) to the east of the Valles Marineris into which converge several of the largest outflow channels on the planet. It was chosen as the landing sites for both Viking 1 and Pathfinder because of the abundant evidence for water erosion.
Columbia Hills—A group of hills (14.6°S, 175.5°E) to the southeast of Mars Exploration Rover Spirit’s landing site dedicated to the seven astronauts from the space shuttle Columbia. The rocks of the hills are highly variable both in their origin and in their degree of alteration, ranging from unaltered, olivine-rich rocks that retain all their primary volcanic minerals to sulfate-rich, hydrated mineral-rich rocks with almost no primary minerals remaining.
Echus Chasma—A north-south box canyon (5°N, 280°E) located north of the Valles Marineris. It is closed to the south and open to the north. The canyon may have been the source of the floods that formed Kasei Vallis, the largest outflow channel on the planet.
Elysium—The second largest volcanic region on the planet centered at 25°N, 145°E.