NASA's Mars Exploration Rover Spirit used its rear hazard avoidance camera to take this view toward the south during the 1,899th Martian day, or sol, of Spirit's mission on Mars (May 6, 2009).
The foreground shows that Spirit's left-rear wheel (on the right from this viewpoint) churned up bright-toned material when the rover was becoming embedded at this position, but that the right-rear wheel did not.