text: Opportunity arrives at Spirit of Saint Louis crater and peers into Marathon Valley and Endeavour crater from current location on Mars as of April 3, 2015 in this photo mosaic. The crater, featuring an odd mound of rocks now named Lingbergh Mound, is the gateway to Marathon Valley and exposures of water altered clay minerals. This pancam camera photo mosaic was assembled from images taken on Sol 3973 (March 29, 2015) and colorized. Credit: NASA/JPL/Cornell/ Ken Kremer/kenkremer.com/Marco Di Lorenzo