WHITE ROCK got its nickname when contrasty image processing gave the feature, which measures about 15 by 18 km (9 by 11 miles), a chalky-bright appearance and suggested it was made of water-deposited sediments, like the salty residue of a dried-up desert lake. However, the Thermal Emission Spectrometer (TES) found that White Rock was built of wind-blown dry sediments. The image seen here was taken at visible-light wavelengths by another instrument, the Thermal Emission Imaging System on NASA's Mars Odyssey orbiter. Click on the image to download a larger version (3.4 MB). NASA/JPL/Arizona State University