Spirit has reached the the edge of "home plate", a feature that appeared as a pale circle from orbit. It is also referred to as "Spirit's Burns Cliff" to compare to the layered crater wall found by Opportunity.
[link|http://marsrovers.jpl.nasa.gov/gallery/all/2/n/746/2N192597856EFFAO55P0685R0M1.JPG|http://marsrovers.jp...AO55P0685R0M1.JPG]
[link|http://marsrovers.jpl.nasa.gov/gallery/all/2/p/748/2P192771280EFFAO55P2272L7M1.HTML|http://marsrovers.jp...O55P2272L7M1.HTML]
Some of those rocks look like silvery wood.