This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows several large, dark slope streaks formed on the wall of a trough on the lower north flank of the giant Tharsis shield volcano, Pavonis Mons. The layered rock in the upper wall of the slope shown here is probably volcanic (lava flows). The ancient lava flows and the troughs cut through them have been thickly mantled by windblown dust. From time to time, dry dust avalanches will create streaks such as those shown here. This scene is located near 4.1°N, 111.5°W, and has been rotated such that north is toward the bottom, west to the right. Sunlight illuminates the scene from the right/lower right. The picture covers an area approximately 0.8 km (1/2 mile) wide by about 1.7 km (~1 mile) long.