The Mars Global Surveyor first imaged fresh-appearing gullies on steep slopes. They appear relatively young — perhaps a few million years old — because they have few impact craters. Scientists are actively investigating these features to determine whether relatively recent discharges of water may have been involved in their formation.
The combination of an alcove, channel, and fan suggests that water or a water-charged debris flow carved these gullies, but dry avalanches could also be responsible.
Mars Global Surveyor, MOC
NASA/JPL/Malin Space Science Systems image