NASA's Mars Exploration Rover Spirit has been analyzing sulfur-rich rocks and surface materials in the "Columbia Hills" in Gusev Crater on Mars. This image shows rocky debris and dust, which planetary scientists call "regolith" or "soil," that has been churned up by the rover wheels. This 40-centimeter-wide (16-inch-wide) patch of churned-up dirt, nicknamed "Paso Robles," contains brighter patches measured to be high in sulfur by Spirit's alpha particle X-ray Spectrometer. Spirit's panoramic camera took this image on martian day, or sol, 400 (Feb. 16, 2005). The image represents the panoramic camera team's best current attempt at generating a true color view of what this scene would look like if viewed by a human on Mars. The image was generated from a combination of six calibrated, left-eye images acquired through filters ranging from 430-nanometer to 750-nanometer wavelengths.