The "White Rock" inside Pollack Crater (NASA/JPL/MSSS)

Caption NASA originale:"White Rock" is a ridged mound that was first seen and informally named "White Rock" in pictures from the Mariner 9 orbiter in 1972. In black-and-white photos, the feature appears much brighter than its surrounding terrain, giving the impression that the material is white. Later analyses of Mariner 9, Viking and MGS data showed that the feature isn't actually white: it is somewhat red and reflects only about 20-25% of the sunlight that falls upon it (a white surface would reflect 100%). Located in Pollack Crater, a 95 Km wide impact basin at 7.9°S, 334.7°W, White Rock is the light-red/orange feature with the rectangular white box drawn on it in the context view. The light-toned material that gives White Rock its name forms steep cliffs with valleys between them covered by dark, windblown, rippled sand".