The Colorado River Basin is home to some very, very rare Native Indian Intaglios. They are large images carved into the ground. They are best seen from the air, so taking a picture doesn't do it justice. The picture above is of a human form that is about 80 feet long. The Colorado River Basin left a layer of dark black rocks that once dug out leave a very pale sandy image. These date from 450 to 1000 years ago. They believe they were used as ceremonial sites, but nobody knows for sure.