I’m self-employed http://www.keandra.com This fan is on the inside of the rim of Mojave Crater, a 60-kilometer-wide (40-mile-wide) impact crater near the equator of Mars. The structure matches an Earthly alluvial fan almost perfectly. Larger boulders are heavier and can’t be carried as easily by floodwaters, so they tend to stop soon after the terrain levels out. Smaller rocks can travel farther, which appears to be the case here. The branches, the shape, the direction: Everything indicates a flash flood on Mars.