These maps of a region in Mawrth Vallis, Mars, were created from data captured by the CRISM spectrometer on October 2, 2006. It covers an area about 13 kilometers long and, at the narrowest point, about 9 kilometers wide. At the center of the image, spatial resolution is 35 meters per pixel. The leftmost image shows the view in approximately true color; the second image is the same region in a set of infrared wavelengths. The right-side images are maps of areas whose spectral properties match the spectral properties of minerals as measured in a laboratory on Earth. The first spectral map shows the distribution of iron-rich clays; the second spetral map shows the distribution of aluminum-rich clays. The iron-rich clays correspond with a layer of rock that is dark red in the true-color view and bright gray in the infrared. In addition, CRISM found previously undetected exposures of aluminum-rich clay, in a rock unit that is buff-colored in the true-color view, and bluish in the infrared view. Both rock types formed early in Mars' history, about 3.8 billion years ago. The difference in clay mineralogy reveals differences in the environment in which the rocks formed. Those differences may mean that the environment changed over time, or they may mean that there were local environmental variations on small scales, over distances of a few kilometers.