Aha!

You spotted it, Robert. "something heavy"...

My model for these dune "channels" is that in the winter, an icepack (CO2, of course), forms on the crests of the highest dunes or as a corniche or overhang.

In the spring this thaws, and huge lumps of solid CO2 fall off the crest and glissade down the hill on a cushion of boiling CO2, ploughing the sand aside as they do so.

At the bottom, they stop and form those distinctive closed depressions at the end of the trails.

Sometimes the lumps of ice skip and roll, making the trails that "twitch" and "jog". Sometimes they just slide and bulldoze.

Because each trail has a raised rim of bulldozed sand, nearby trails tend to avoid each other, thus the parallel pattern, rather than dendritic...