A steep fan at Coprates Catena, Valles Marineris, Mars, as seen by HRSC data

We investigate a steep fan‐like deposit in the Coprates Catena region, using the new High Resolution Stereo Camera (HRSC) data and other Martian data sets. Water flowing in a 45‐km‐long sapping valley entered a deep trough and formed a stepped fan 1100‐m‐high above the trough floor with a mean slope of 7.4°. The origin of the fan is uncertain. However, we favor an alluvial, sheetflood‐dominated deposition for the sedimentary feature, though there is weak evidence for a possible stationary water level (∼500 m above the floor) and a fan‐delta origin. Regional morphotectonics and previous geological mapping suggest that groundwater‐related aqueous sedimentation could have been active from Hesperian to Early Amazonian implying favorable climatic conditions for the flow and possible ponding of water during that period.