A thought about the raised sides of the dune channels- water evidence?
Water expands when it freezes. Water flowing though sand dunes would cut a channel, and some of the water would soak into the side of the channel like a sponge. On Mars, that water would freeze, expand, and raise the rim of the channel.
Does CO2 expand when it freezes? Most elements shrink when they freeze.
I am not sure about CO2 going from a liquid to a solid. If it doesn’t expand then I would say these channels had to be carved by water, and that the raised rims of the channels were caused by liquid water soaking in, freezing and expanding.