Near Wupatki National Monument (the site of an ancient Pueblo ) is Sunset Crater National Monument, the site of a comparatively recent (in geologic terms) eruption. I actually came upon it by accident, taking a side trip to visit Wupatki.  Of course, I was immediately struck by the beauty of the Quaking Aspens growing in the volcanic rock, and took this photo. But at the same time, I couldn’t help but think of a basic principle of geology: the rock cycle. You may recall that the rock cycle is the process rock goes through during its lifetime. It begins with magma, from which igneous rocks (such as basalt) are formed. Those rocks may erode, form sediments, and eventually form sedimentary rocks which, under heat…