Between the grabens and the adjacent lowlands, isolated remnants of what was once a continuous rock layer mark the landscape. These erosion-resistant remnants come in different shapes – some appear as rounded hills known as knobs, while others have flat tops and resemble small plateaus called mesas. Interestingly, many of them are partially surrounded by lineated valley fill material, which seems to have traveled all the way down to the lowlands. The knobs are most prominent on the right side (north) of the image. Toward the center and left-hand side, they gradually become fewer – and eventually disappear. All around the knobby terrain small, narrow meandering channels mark the surface (see annotated image). Meandering channels have a serpentine morphology formed by erosion and sedimentation of material.

The left side of the scene looks much smoother, which may point to a different geological origin. One possibility is that this smoother material may be linked to the massive landslides triggered by the collapse of Olympus Mons’ flanks forming its Aureole (see annotated image). If that is the case, the debris would have traveled a huge distance to reach the foot of Acheron Fossae.