The Martian wind has cut deep crevasses into this crater in the Terra Cimmeria region. The edges of these dunes look sort of like fins in this new image from the HiRISE camera on the Mars Reconnaissance Orbiter. But the fins are actually double "horns" where the wind from the East hit the dunes. You can also see "dark, sinuous forms" where Martian "dust devils" pushed away the brighter dust and uncovered the darker surface. Click through for another image.

[HiRISE]