Image of the 3 most famous rocks of Monument Valley (left to right): Left Mitten, Right Mitten and Merrick Butte. Monument Valley is not really a valley. The tops of the mesas mark what was once a flat plain. Millions of years ago, this plain was cracked by cataclysms within the earth. The cracks widened and eroded, until all that is left today are the formations rising from the desert floor. Thank you for stopping by and checking my work!