One of the most impressive geologic features in Montana is the mountainside north of this location. There is a prominent layer of white limestone halfway up the mountainside. The rocks above this layer were deposited more than 50 miles southwest of here and moved here as part of the Lewis Thrust Sheet-an enormous slab of Precambrian-age sediments more than a mile thick that encompasses most of today’s Glacier National Park. The Lewis Thrust Fault on which the thrust sheet moved is under the whitish limestone layer and is a thin zone of intensely sheared shale. Movement of the Lewis Thrust Sheet and the many other thrust sheets in the area occurred between 72 and 58 million years ago as the Rocky Mountains were forming. The “motor” causing the Rock Mountains to form was the subduction of an oceanic plate-the Farallon Tectonic Plate-under the western margin of North America.
To log this Earthcache please send me an email with the text "GC2EVQK The Lewis Overthrust Fault” on the first line and the answers to the following questions (The answers can be found on the informational sign and by making observations about the surrounding geology. Please do not post answers in your log.)
1. Why are the sedimentary rocks on the mountainside “out-of-order”?
2. What is argillite?
3. What is the age of the fossils above the thrust fault?
4. Looking at your GPS, what does it say the elevation is at the posted coordinates?
5. What do you estimate the elevation of the white limestone on mountainside north of you is?
After sending your email go ahead and log this Earthcache as a find. I will only respond if you have incomplete logging requirements. Any logs submitted without completing the additional logging requirements will be DELETED.