Douglas Jerolmack of the School of Arts & Sciences says, “Knowing whether pebbles in a river moved 1 kilometer or 100 kilometers [0.6 miles or 62 miles] could tell us how stable water was on the surface of ancient Mars.”
http://www.csmonitor.com/Science/2015/1014/Did-Mars-once-have-rivers-The-pebbles-say-yes Christian Science Monitor