To log the cache email me the answers to the following questions. Please send them close together, if you don't your log may be deleted because I cannot match them up.
- Send the Name, or GC code, and the names of people that were with you that you are submitting the answers for.
- If you look to the south you should be able to identify an pothole arch on the hill. Do you think it formed from the top of the hill or lower down?
- Did the pothole break through an alcove, or did it break out the side of the mesa, or perhaps both. Explain why you think so.
- Does the sandstone look even (making it Entrada Sandstone) or rough and blocky (making it Dewey Sandstone)
- Because of cheating, please post a photo of yourself or paper with your caching name, or foot, whatever, with the valley or road in the background. (not the arch)
The Geology in Front of You.
In front of you, you can see a large mound of sandstone, left over from ancient dunes this is part of the Navajo sandstone. The Navajo sandstone is about 300 to 600 feet thick. It is often a cross bedded sandstone because it is made up of petrified dunes. It makes up the base of most of the formations down this road.
On top of that is the Dewey Bridge member of the Carmel foundation. It is made up of sediments and sometimes has some different colors based on the makeup of the rocks. Because the sand is not as evenly distributed it cracks and tends to look blocky. Kind of like a horrible brick job using different kinds of bricks. This is between 40-200 feet in thickness. Depending on where you parked you may not be able to see much of this.
On the very top of the hill is Entrada Sandstone. It is another thick group of stone that is 200-500 feet thick. It makes up most of the visible mesa/butte that is in front of you.
Potholes are formed in many kinds of stone. They can be formed by water and wind blowing sand particles in a small pocket. The pocket is eroded deeper and larger. Biological activity can live the water and help to erode the sandstone as well. The bacteria can help seal the sides of the pothole making it erode deeper. In fact as my family and I hiked in the fall we could hear the frogs croaking in the potholes.
Combine the Two
Eventually the potholes can get deep enough and long enough to break out and form an arch. They can break out through an alcove, and it would basically just be a hole, or they can start to find cracks and break out into the smallest side. Then they can wear into some of the other arches that you can see around the park.