Data and pictures from NASA’s Mars Reconnaissance Orbiter (MRO) suggest that gullies that recently formed in some Martian craters were not created by liquid water. The gullies had formed in crater walls some time between two sets of Mars Global Surveyor images taken several years apart, and scientists speculated that groundwater leaking out the side of the crater could have caused the gullies. However, more detailed observations by MRO now argue that the gullies were formed by landslides of loose, dry material.
NASA Orbiter Provides Insights About Mars Water and Climate

HiRISE – Science in Motion