After months of traveling across a cratered plain, NASA's Mars Exploration Rover Spirit took this image of a large, continuous rock outcrop at the base of the "Columbia Hills." The image was taken on sol 189 (July 15, 2004) with the rover's rear hazard-avoidance camera. Spirit's left rear wheel is visible in the image, along with rocks that have a somewhat layered appearnce.

The rover drove over this area backward on five wheels -- a new strategy that will conserve the rover's sixth, aging wheel for those times when it is needed most. Spirit is on its way to the north-facing slope of the hills, where it can look at rock outcrop in more detail, using more solar power.