English: Pit chain in Tractus Fossae (Tharsis) from MGS MOC release 2-620, 1/29/2004. This January 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a chain of pits formed in a trough of the Tractus Fossae region near 24.1°N, 103.4°W. The troughs are graben, which are formed by faults cutting rock as the crust is stretched and extended, in this case toward the east and toward the west (right and left). As the rocks broke and moved along the fault lines that create the sharp cliffs on either side of the troughs, some materials between the trough walls collapsed along the fault trend to form the chain of pits. The picture is 10.5 km long and 3.2 km (1.9 mi) wide. North is to the top and somewhat to the right. Sunlight illuminates the scene from the lower left.