Along the route from Grand Canyon National Park to Petrified Forest National Park there are two small, but worth visiting National Monuments. In Wupatki there are some masonry pueblos (or villages) that ancestors of today's Hopi and Zuni Indians built here around the year 1100 (and they did not speak English). The area was and still is geologically active. Sunset Crater National Monument displays some of the more impressive volcanos in the area, but if you drive to Flagstaff you can see many more of them (I was quite surprised about that).