Geocaching - The Official Global GPS Cache Hunt Site

Directions:

South Window

From Hwy. 191 enter Arches National Park. You should stop at the Visitors’ Center on the way into the park to pick up descriptive pamphlets and see the exhibits. Do not miss the excellent film shown in the new auditorium that describes the geology of rock arches.

Follow the road past Balanced Rock, turning right at ~9.2 mi. Proceed another 2.5 mi. to the parking area. The trail goes to the North and South Windows and Turret Arch.

Supplies: Water, sunscreen, camera.

Alcove: An Arch "Wanna'be"

Learning Objectives:

1. To become familiar with the terms “fins”, “joints” and “evaporite”.
2. To understand how arches and alcoves are formed.

Fins on a TOPO Map

The Entrada Sandstone lies atop a massive body of salt that formed in the Paradox Basin ~250 million years ago. The salt is water soluble and plastic. It migrated as the weight of deposited sediments pressed down on it. The overlying rocks bowed upward into an inverted “U” (an anticline). Under this stress the sedimentary rock fractured into parallel slices known as "fins". The fractures are called "joints", weakened places subject to erosion.

Alcoves and arches form as these sandstone fins are worn away by chemical weathering (dissolution of the calcium carbonate that cements the sand grains) and mechanical weathering (water, wind, ice, abrasion)

Educational Requirement: To get credit for this EarthCache you must email us your answer to any one of the Study Questions and let us know how many people were in your party.

Study Questions: ("Azimov-rated"). Note: Graduate- and Ph.D.-level questions may take a bit of looking on the www.

1. College-Bound AP Describe how “fins” were formed.
2. College-Bound AP (Virtual survey) Double-click on the cache map above and select the "hybrid" or "satellite" view in Google Maps. As you zoom in on the cache, look for evidence of fins nearby?
3. College-Bound AP Describe the forces that erode fins.
4. Freshman Do you think differences between the two members of the Entrada sandstone contribute to the formation of the arches?
5. Graduate Where did the salt in the Paradox evaporite beds come from?
6. Ph.D. What chemical compounds (minerals) are included under the general term “evaporites”?
7. Ph.D. As you pass the intersection of Hwy. 279 and Hwy. 191 north of Moab there is a sign which exists because of the Paradox Evaporites. What does it say? Explain. [Major hint!]

Links and Resources:

1. Wikipedia on Salt Domes
2. Wikipedia on Evaporites
3. How arches are formed.
4. Park Service Descriptions
5. Technical paper
6. Really technical paper
7. Anticlines, synclines and monoclines.