Chasma Boreale is a large valley the cuts into Mars' north polar cap and layered materials. At the uppermost portion of this valley (84.9 degrees north, 356.6 degrees west), its head is marked by a kilometer-high (3,000-foot-high) escarpment that allows seeing the subsurface layering and how the layers extend to nearby sloping surfaces that also cut into the materials. The floor of Chasma Boreale is a cratered plain that has sand on it. In part the sand appears to be eroding out of the escarpment. This image by the Context Camera on NASA's Mars Reconnaissance Orbiter was taken in support of observations by two of the orbiter's other instruments -- the orbiter's Compact Reconnaissance Imaging Spectrometer for Mars and the High Resolution Imaging Science Experiment -- presented at an Oct. 16, 2006 news briefing. Further details can be found at http://mars.jpl.nasa.gov/mro/.