Today's Image of Mars shows a segment of Olympica Fossae, as taken by HiRISE.
Olympica Fossae is a 420km long set of troughs, or fossae, in the Tharsis Quadrangle on Mars. Fossae are created when the crust stretches and fractures along two parallel faults. When this happens the area between the two faults sinks down and forms a trough.
Scientists speculate that at one point in the Martian past the troughs of Olympica Fossae served as outflow channels, redirecting floods of water, while at another point they served as channels for lava. This is possible because Mars has experienced many different climates over the past few billion years.
Because HiRISE has yet to caption this image, clicking on it will take you to a map of Tharsis Quadrangle showcased by Mars Travel.