Gullies on steep slopes are found in certain regions of Mars.
 Many ideas have been advanced to explain them.
 Formation by running water when the climate was different is a popular idea.
 Recently, because changes in gullies have been seen since HiRISE has been orbiting Mars, it is thought that they may be formed by chunks of dry ice moving down slope during spring time.
 Gullies are one of the most interesting discoveries made by orbiting space craft.
Gullies on steep slopes are found in certain regions of Mars.  Many ideas have been advanced to explain them.  Formation by running water when the climate was different is a popular idea.  Recently, because changes in gullies have been seen since HiRISE has been orbiting Mars, it is thought that they may be formed by chunks of dry ice moving down slope during spring time.  Gullies are one of the most interesting discoveries made by orbiting space craft.
Noachis quadrangle