It may take a while to load, but the detail on this one is important. This is an
Astronomy Pic of the Day pic showing some of the surface of Mars from orbit.
Why this is cool: it sure looks like those formations came from water, doesn't it? And on Earth, similar formations are generally caused by water. So they feel these images are further evidence of underground water on Mars. Not at all far underground, either; 30-60 centimeters.
Note that the above image is 1500 meters across.