If you continue East along the Historic Route 66 are, you find the Petrified Forest National Park. It is an entire forest that had been petrified, leaving behind what look like fallen trees -- the petrified forest. They have a pretty simple, but nice, visitors center with a video explaining how the petrified wood is formed and some of the history of the park.
From there, we hiked some simple trails to see the colorful and incredible artifacts. Very interesting.