Missing bedrock

A piece of Mars: Wind flow on Mars can be quite dramatic. Here, a single wind-sculpted hill stands 1.5 km (0.93 mi) wide and 600 m (1970 ft) high (color shows elevation). That sounds big, but vastly larger is the volume of material that has been removed to form it. A sandy ridge forming a “bow shock” indicates present-day winds still blow in the same direction. (HiRISE ESP_017173_1715, NASA/JPL/Univ. of Arizona)