Blade-Like Martian Walls Outline Polygons

This view shows part of an area on Mars where narrow rock ridges, some as tall as a 16-story building, intersect at angles forming corners of polygons. The area covered in the image spans about two-thirds of a mile (1.1 kilometers) wide, in the Gordii Dorsum portion of the Medusae Fossae region of Mars. The image is from the High Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter. North is up. Note the shadows cast by some of the walls. These ridges likely formed as lava that hardened underground and later resisted erosion better than the surrounding material. From ground level, they would resemble hardened-lava walls on Earth http://photojournal.jpl.nasa.gov/catalog/PIA21264