Slope Streaks in Acheron Fossae on Mars . ... Credit Copyright: HiRISE , MRO , LPL (U. Arizona) , NASA Explanation: What creates these picturesque dark streaks on Mars? ... A leading hypothesis is that streaks like these are caused by fine grained sand sliding down the banks of troughs and craters. Pictured above , dark sand appears to have flowed hundreds of meters down the slopes of Acheron Fossae . ... Acheron Fossae is a 700 kilometer long trough in the Diacria quadrangle of Mars. ...