Alluvial fans are found on Earth, Mars, and even Saturn’s moon, Titan. Roddy Crater on Mars is home to several large alluvial fans, which formed as water moved sediment from the mountainous crater rim and deposited it onto the flatter crater floor.
The fans built up over time during intense rain storms or from melting snow. Due to the strong winds on Mars, the river channels that once carried water and sediment on the fan surfaces are now standing as raised ridges and platforms. A thin blanket of ejecta (upper right) from a small crater on Roddy’s eastern rim protected underlying fan surfaces from modification by the wind compared to nearby, unprotected fans (left). The scarp beneath the thin ejecta surface exposes beautiful… [More at link]