Cuesta morphology a) sketch of cuesta landform. Cuestas occur in areas of tilted strata and are caused by the differential erosion of the harder top layer and the underlying layer that is weaker and therefore more erodible (figure after Castiglioni 2000). b)−c) Examples of cuestas on the Agilkia site (indicated by black arrows). The hard layer probably consists of material poor in volatiles, whereas the soft underlying layer is richer in volatile material and therefore more erodible by sublimation. NAC image acquired onb) 2014-09-14 at 17:32:15 in near-IR filter and on c) 2014-11-12 at 16:08:51 in orange filter.