Eons ago this area was covered repeatedly with sand either via streams, huge inland lakes and sea or via wind. These were compressed and gradually uplifted. At this point the Colorado River drainage started to work. The simplified explanation for all the fantastic shapes is the harder area of sandstone erode more slowly than the softer ones.
Top right is the formation known as the Coke Ovens. At one time they were one solid ridge between two canyons. They have eroded now into shapes that look very much like actual coke ovens hence the name. They are formed of Wingate Sandstone softer rock than the Kayenta Caprock that has finally eroded away.
Top left is a shot where I am trying to capture the small arch on the canyon wall on the left of the image. The background mountains are the book cliffs. While parts of Colorado National Monuments contain Morrison formation Sandstone (which is a treasure trove of fossils) the bookcliffs were laid down during the early days of Mammalian domination.
