Collapse Pit in Tractus Fossae

This HiRISE image shows a Collapse Pit in Tractus Fossae, a Region of large ridges and troughs created by tectonic activity.
The "Fossae" occur on the Tharsis Volcanic Rise, a giant Region of enhanced volcanic activity that includes the three large volcanoes Ascraeus Mons, Pavonis Mons and Arsia Mons.
The Pit in this image has very steep walls, and so only a narrow arc is illuminated by Sunlight. The rest of the Pit is in dark shadow. However, a stretched version of the image shows details of the pit floor, due to a small amount of scattered Sunlight.

Pits like this form by collapse into underground voids, such as those left by propagating magma-filled dikes. They may sometimes have overhanging walls, although in this case the walls can be seen and appear nearly vertical. Some similar features are found on Earth: Devils Throat, in Hawaii, is one example. Other similar examples have been imaged on Mars as well.