Here is what the THEMIS people have to say about "White Rock:"

"White Rock is the unofficial name for this unusual landform which was first observed during the Mariner 9 mission in the early 1970's. As later analysis of additional data sets would show, White Rock is neither white nor dense rock. Its apparent brightness arises from the fact that the material surrounding it is so dark. Images from the Mars Global Surveyor MOC camera revealed dark sand dunes surrounding White Rock and on the floor of the troughs within it. Some of these dunes are just apparent in the THEMIS image. Although there was speculation that the material composing White Rock could be salts from an ancient dry lakebed, spectral data from the MGS TES instrument did not support this claim. Instead, the White Rock deposit may be the erosional remnant of a previously more continuous occurrence of air fall sediments, either volcanic ash or windblown dust. The THEMIS image offers new evidence for the idea that the original deposit covered a larger area. Approximately 10 kilometers to the southeast of the main deposit are some tiny knobs of similarly bright material preserved on the floor of a small crater. Given that the eolian erosion of the main White Rock deposit has produced isolated knobs at its edges, it is reasonable to suspect that the more distant outliers are the remnants of a once continuous deposit that stretched at least to this location. The fact that so little remains of the larger deposit suggests that the material is very easily eroded and simply blows away."

"Scientists know that you can’t always trust what your eyes see alone. You have to use other kinds of science instruments to measure things that our eyes can’t see . . . things like information about what kinds of minerals make up the landforms. Mars scientists once thought, for instance, that these unusual features might be vast hills of salt, the dried up remains of a long-ago, evaporated lake."

"Not so, said an instrument on the Mars Global Surveyor spacecraft, which revealed that the bright material is probably made up of volcanic ash or windblown dust instead. And talk about a cyclical "ashes to ashes, dust to dust" story! Particles of this material fell and fell until they built up quite a sedimentary deposit, which was then only eroded away again by the wind over time, leaving the spiky terrain seen today. It looks white, but its apparent brightness arises from the fact that the surrounding material is so dark."

Can we move on now?