This image shows the wall of a scuffmark NASA's Curiosity made in a windblown ripple of Martian sand with its wheel. The upper half of the image shows a small portion of the side wall of the scuff and a little bit of the floor of the scuff (bottom of this image). The prominent depression with raised rims at the bottom center of the image was formed by one of the treads on Curiosity's front right wheel.
The largest grains in this image are about 0.04 to 0.08 inches (1 to 2 millimeters) in size. Those large grains were on top of the windblown ripple and fell down to this location when the scuff was made. The bulk of the sand in the ripple is smaller, in the range below 0.002 to 0.008 inches (50 to 200 microns).
The full scuffmark is 20 inches (50 centimeters) wide, which is the width of Curiosity's wheel.
This image from the Mars Hand Lens Imager (MAHLI) is the product of merging eight images acquired at eight slightly different focus settings to bring out details on the wall, slopes, and floor of the wheel scuff. The merge was performed onboard the MAHLI instrument to reduce downlinked data volume.
The image was acquired by MAHLI with the lens about 4.7 inches (12 centimeters) from the target. The pixel scale is about 0.002 inches (50 microns) per pixel. The image covers an area, roughly 3 by 2 inches (8 by 6 centimeters). The image was obtained on Oct. 4, 2012, or sol 58, the 58th Martian day of operations on the surface.
Image credit: NASA/JPL-Caltech/MSSS