The NASA Mars Reconnaissance Orbiter spacecraft beamed back images that scientists have used to create a 3-D reconstruction of ancient water channels below the surface of Mars – see www.jpl.nasa.gov/news/news.php?release=2013-087&cid=release_2013-087
The continental flooding event they have pieced together from the geology is comparable to the channelled scablands in the Pacific NW, in eastern Washington State. The rate of erosion was previously underestimated. They used orbital sounding radar in order to understand how water has shaped the surface of Mars. Extensive volcanic activity buried evidence of Mars older geology including the width and most of the length of the channel system. There are other ancient channels on Mars, also formed by catastrophic movement of ground water (it is theorised). The 3-D image can be viewed at www.jpl.nasa.gov/spaceimages/details.php?id=PIA16767 and for the spacecraft concerned, visit www.nasa.gov/mro