5.
Here you can see at close hand the difference between the dark, upper layers of ocean sands and the light color of the lower and earlier stream and dune sands. Look here at the cliff above you and a little to the right. The lower is Zuñi sandstone, of the Jurassic period, and forms the bulk of El Morro. The upper is Dakota sandstone of Cretaceous period, representing beach deposits of the ancient sea which covered all the area. The contact surface between these two units represents a time interval of between 25 and 50 million years when erosion instead of new deposition was taking place.