Some features on Mars seem to be in the process of being uncovered.
 So, the thought is that they formed, were covered over, and now are being exhumed as material is being eroded.
 These features are quite noticeable with craters.
 When a crater forms, it will destroy what's under it and leave a rim and ejecta.
 In the example below, only part of the crater is visible.
 if the crater came after the layered feature, it would have removed part of the feature.
Some features on Mars seem to be in the process of being uncovered.  So, the thought is that they formed, were covered over, and now are being exhumed as material is being eroded.  These features are quite noticeable with craters.  When a crater forms, it will destroy what's under it and leave a rim and ejecta.  In the example below, only part of the crater is visible.  if the crater came after the layered feature, it would have removed part of the feature.
Ismenius Lacus quadrangle