NASA's Mars Exploration Rover Spirit collected data on morphology, composition, and mineralogy of a rock nicknamed "Tetl" using the microscopic imager, the alpha particle X-ray spectrometer, and the Moessbauer spectrometer before moving on. Scientists are discussing a suggestion that this rock outcrop and others on the "West Spur" of the "Columbia Hills" in Gusev Crater on Mars may contain evidence of graded bedding, in which alternate layers of sediment are either coarser or finer depending on the turbulence of the processes that deposited them. Such layers could be deposited by water circulating in rivers or lakes, volcanic ash settling on the surface, wind carrying fine-grained sediments, or a combination of these processes. This view is a mosaic of images that Spirit took with its microscopic imager on the rover's 272nd and 273rd martian days, or sols (Oct. 7 and 8, 2004). It has been enhanced to bring out details in the shadows without washing out sunlit areas. The section of rock shown here is approximately 17 centimeters (6.7 inches) wide.