This view from NASA's Mars Exploration Rover Opportunity shows part of 'Marathon Valley,' a destination on the western rim of Endeavour Crater, as seen from an overlook north of the valley. The scene spans from east, at left, to southeast. It combines four pointings of the rover's panoramic camera (Pancam) on March 13, 2015, during the 3,958th Martian day, or sol, of Opportunity's work on Mars. The rover team selected Marathon Valley as a science destination because observations of this location using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on NASA's Mars Reconnaissance Orbiter yielded evidence of clay minerals, a clue to ancient wet environments. Opportunity has been exploring the Meridiani Planum region of Mars since January 2004. This version of the image is presented in approximate true color by combining exposures taken through three of the Pancam's color filters at each of the four camera pointings, using filters centered on wavelengths of 753 nanometers (near-infrared), 535 nanometers (green) and 432 nanometers (violet).