It's been a while since I checked in at the UA HiRISE web site to see what new images are coming back from the Mars Reconnaissance Orbiter. And as they often are, there are some amazing pictures. This one of Cerberus Fossae looks like a channel full of clear blue water. The HiRISE Science Team has this to say about it:
This small fossa segment cuts the channel of Athabasca Valles, and post-dates the youngest of Mars' outflow channels. A "fossa" is a cavity or depression.
Floods of water and lava are thought to have emanated from the larger fossae nearby, perhaps forming the Athabasca channel and later filling it with lava. Comparison with the larger fossa segments at the Athabasca Valles head may reveal whether this will be a source of a future flood.