Lumpy bumpy dunes

A piece of Mars: These funny shaped dunes were formed by winds blowing from two directions – one from the top of the frame and one from the upper right. Both winds make steep slopes (slip faces) on the downwind (lee) sides of the dunes. With enough sand supply, the “point” between the slip faces will continue to extend toward the lower left as the two winds take turns driving the sand back and forth. (HiRISE ESP_037203_2555, NASA/JPL/Univ. of Arizona)