Today's Image of Mars is from HiRISE and it shows a spectacular fluvial fan on a crater floor. The fan begins where a channel enters the crater, which suggests that it was a delta.
Deltas are formed when water enters a larger space and spreads out. When spreading out the water begins to move at a slower pace and many sediments that were caught up in the fast moving water begin to sink. Eventually those sediments sink and become deposits.
This image is further evidence that water once existed in abundance on Mars. By studying the image and others like it scientists hope to gain a better understanding of the Martian past and eventually discover what happened to all the water on Mars.
I'm actually surprised that conspiracy theorists haven't jumped on this one because the delta "looks like the side profile of a head" or something ridiculous. Just another natural formation here!
Clicking on this image will take you to the original, captioned image from HiRISE.