"White Rock": An eroded Martian lacustrine deposit(?)

The existence and location of ancient lake sites and sediments have important implications for Martian paleoclimate and exobiology. White Rock, an enigmatic crater interior deposit, may be the eroded remnant of such a lacustrine deposit. Stereogrammetric analysis of newly processed Viking images allows better determination of the dimensions of White Rock (12.5 x 15 km, thickness 180 to 540 m, volume ∼40 km 3 ), reveals differences in erosion patterns that may reflect differences in depositional environment, and allows the identification in or on the crater wall of a possible source region of the high-albedo White Rock material. If White Rock is the remnant of a once-larger deposit, then open- system circulation may have been required to deliver the required quantity of evaporites.