Orcus Patera

Orcus Patera is a region on the surface of the planet Mars first photographed by Mariner 4. Of unknown formation, whether by volcanic, tectonic, or cratering causes, the region includes a depression about 380 kilometres (240 miles) long, 140 kilometres (87 miles) wide, surrounded by a rim up to 1.8 kilometres (1 mile) high.