Sol 4016, May 12, 2015. Five Navcam frames composited show the western horizon from south (left edge) to north (right edge). Opportunity is resting on the material that fills Spirit of St. Louis Crater, which erosion has all but erased. The crater’s infill is visible as a darker surface edged by a unit made of lighter-toned sediments.
Although sand dune ripples overlie much of the scene, the contact between the two units can be traced as it curves from the left foreground around to the middle distance at right. (Click the image to open a larger version in a new browser tab.)
Opportunity raw images, its latest mission status, a location map. and atmospheric opacity, known as tau.