Sounds like permafrost to me.
Should it be studied as such?
Are there characteristics of permafrost that would be visible with the instruments now in orbit?
Does this preclude the idea of CO2 saturation in the permafrost?
Maybe the CO2 that is the atmosphere indicates that there is really not enough to account for the erosion, but just that is the last gas available because of the long harsh history of Mars?
Just a few thoughts.
Ed