Is it windblown or not?
A Piece of Mars: This scene is 0.96×0.54 km (0.60×0.34 mi) across. There’s an old river valley running across it. The walls of the valley have been eroded and there’s a washboard pattern with a wavelength of ~6m (20 ft). When I first saw this image I thought it was exposed, tilted layers, but a closer look reveals a much smaller (and younger) set of ripples that are similarly oriented and almost certainly formed by the wind. What do you think? (HiRISE ESP_041982_1535, NASA/JPL/Univ. of Arizona)