hard ridges behind. Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Water here could have supported past life in these locations. Clay may also preserve fossils or other traces of past life. Pingos Pingos are believed to be present on Mars. They are mounds that contain cracks. They contain pure water ice, so they would be a great source of water for future colonists on Mars Mesas Fractures forming blocks In places large fractures break up surfaces. Sometimes straight edges are formed and large cubes are created by the fractures. Glaciers Gallery Interactive Mars map Map of quadrangles For mapping purposes, the United States Geological Survey divides the surface of Mars into thirty "quadrangles", each named for a prominent physiographic feature within that quadrangle. The quadrangles can be seen and explored via the interactive image map below. See also Climate of Mars Geography of Mars Geology of Mars Impact crater List of craters on Mars List of quadrangles on Mars References External links High resolution video by Seán Doran of overflight of a layered area in Arabia Terra Terrae on Mars Arabia quadrangle Mare Acidalium quadrangle