These are grasses in Yellowstone National Park. Ruth and I explored the park in 2010.
We had several other choices from that trip -- a pine log scrimshawed by pine bark beetles almost made it as the cover -- but Ruth liked the way the grasses flowed in this one, and the play of light and shadow.
For the interior, I cut this image into as many slices as there were sections, and headed each section with a different slice -- grayscale, of course.