Warrego Valles is an ancient river valley in the Thaumasia quadrangle of Mars, located at 42.2° south latitude and 93° west longitude. It is 188 km long and was named after a Modern Australian River.
Mariner 9 and Viking Orbiter images, showed a network of branching valleys in Thaumasia called Warrego Valles. These networks are evidence that Mars may have once been warmer, wetter, and perhaps had precipitation in the form of rain or snow. At first glance they resemble river valleys on our Earth. But sharper images from more advanced cameras reveal that the valleys are not continuous. They are very old and may have been eroded. A picture below shows some of these branching valleys. A study with the Mars Orbiter Laser Altimeter, Thermal Emission Imaging System (THEMIS) and the Mars Orbiter Camera (MOC) support the idea that Warrego Valles was formed from precipitation.