First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape.
First discovered in images from Mars Global Surveyor, these features are found on steep slopes, especially on crater walls. They typically have a dendritic alcove at their head, a fan-shaped apron at their base, and a single channel of incision connecting them, giving the gully an hourglass shape.