Some places on Mars show inverted relief.
 In these locations, a stream bed may be a raised feature, instead of a valley.
 The inverted former stream channels may be caused by the deposition of large rocks or due to cementation.
 In either case erosion would erode the surrounding land but leave the old channel as a raised ridge because the ridge will be more resistant to erosion.
 An image below, taken with HiRISE shows sinuous ridges that may be old channels that have become inverted.
Some places on Mars show inverted relief.  In these locations, a stream bed may be a raised feature, instead of a valley.  The inverted former stream channels may be caused by the deposition of large rocks or due to cementation.  In either case erosion would erode the surrounding land but leave the old channel as a raised ridge because the ridge will be more resistant to erosion.  An image below, taken with HiRISE shows sinuous ridges that may be old channels that have become inverted.
Aeolis quadrangle