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.