Monument Valley by Navajo known as Tsé Biiʼ Ndzisgaii, meaning valley of the rocks is a region of the Colorado Plateau located on the northern border of Arizona with southern Utah and lies within the range of the Navajo Nation Reservation. Before human existence, the park was once a vast lowland basin. For hundreds of millions of years, materials that eroded from the early Rocky Mountains deposited layer upon layer of sediments, which cemented over the years into rock, sandstone and limestone. Then a slow and gentle uplift generated by ceaseless pressure from below the surface elevated these horizontal strata quite uniformly one-to-three miles above sea level. What was once a basin became a plateau. Natural forces of wind and water that eroded the land spent the last 50 million years cutting into and peeling away at the surface of the plateau. The simple wearing down of altering layers of soft and hard rock slowly revealed the natural wonders of Monument Valley today. The harder Shinarump formation caps and protects the underlying De Chelly sandstone, which forms the prominent cliffs on mesas and buttes. The softer Organ Rock Shale, found at the base of these cliffs, erode out in stairlike horizontal terraces, forming the sloping foundations of the monuments. Mother Nature continues to shape the land. The changes are so slow it goes unnoticed by humans. Pictured above is the famous Totem Pole formation, this spire monument is an example of what erosion does to a butte.