Madison Limestone...Elephant Rock? EarthCache
Madison Limestone...Elephant Rock?
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I have always called this outcrop of limestone, Elephant Rock, and looked for it on my trips along West Bound I-90 as a landmark. I knew I was about 30 miles from Missoula. It wasn't until I started doing earthcaches that I learned more about Madison Limestone and the Madison Formation.
The coordinates of this cache will take you to a sign that explains how this formation happened and what makes the streaks in the rocks so visible.
It is also a good location to observe pinnacles of Madison Limestone that have been exposed due to erosion. Look to the northern ridge just above the sign.
Geologists define a formation as a thick layer or series of layers of a specific type of sedimentary rock that covers a large geographical area. Formations provide information about what the environment was like in the area when the sediments were being deposited. Because of the types of fossils found in Madison Limestone, geologists think that the sedimients of the Madison Formation were deposited on the floor of a shallow tropical sea. This sediment was laid down during the Mississippian Period of the Paleozoic Era over most of Montana, eastern Idaho, northern Wyoming, and the Dakotas. The Madison Formation is between 1,000 and 2,000 feet thick through out most of Montana which leads geologists to believe this tropical marine environment lasted for many millions of years.
Outcroppings and examples of Madison Limestone can be found in many places through out Montana. They happen to be some of my favorite places: Giant Springs near Great Falls, Lewis & Clark Caverns near Three Forks and Gates of the Mountains near Helena.
To log this cache, email the answers to the following questions:
1. How many years ago was much of Montana submerged under a shallow sea?
2. What color are the streaks in the rock formation?
3. Why does Madison Limestone form such dramatic cliffs and ridges?
Bonus question: Why would I have called this elephant rock?
To learn more about The Madison Formation and take a virtual field trip go to (visit link)
Directions:
Eastbound 1-90 informational sign at Bearmouth Rest Area Mile Post 143 or exit 138 Old Highway 10 Mile Post 10
West Bound I-90 Exit 153 I-90 Frontage Road Mile Post 10
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Treasures
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