The Pryor Mountains are unlike any other landscape in Montana, and utterly different from the Beartooth Mountains only 40 miles to the west. They are geologically, ecologically, meteorologically, and culturally unique – an island of mountains rising from the prairie, formed by erosion of uplifted limestone instead of glacier carved granite. The numerous, rugged and spectacular limestone canyons provide viewpoints from which to share the solitude with the intermittent, quiet and haunting call of the hermit thrush.
Inside Crater Ice Cave, HDR photo by Craig Christopherson
The Pryor Mountains are located on the horizon to the southeast from here. The prominent cliffs and dip slopes are Madison Limestone, which was deposited in shallow seas over 300 million years ago. Along the margins of the mountains, younger tan colored Tensleep sandstone and brick red Chugwater Formation crop out. Canyons in the range expose older rocks, including Pre-Cambrian basement rock more then 2 billion years old. Crustal blocks that form the Pryor Mountains were uplifted along reverse faults about 65-55 million years ago. Over millions of years, water dissolved deep caves in the limestone. Some open vertically to the surface, allowing cold dense air to sink down into the cave. The rock acts as insulator, trapping the dense air and moisture underground, resulting in spectacular ice caves, such as Big Ice Cave. Other caves in the mountains have fantastic formations of stalagmites and stalactites.
To log this Earth Cache, stand at ground zero and answer the following:
1. The Pryor Mountains are primarily composed of what type rock?
2. The three main types of rock are sedimentary, metamorphic and igneous. The main type of rock in the Pryor Mountains falls into which of these 3 categories?
3. The sign at ground zero states the Pryor Mountains are home to ice caves, sinks and caverns which are unique geologic features to the area. Can you see evidence of these at ground zero? Make sure you look to the southeast.
4. View the Pryor Mountains to the southeast. Will the layers at the top be older or younger geologically, from where you stand at ground zero. Justify your answer.
If answers are not sent within 7 days, logs will be deleted.
Sources:
Montana, Information Road Sign at Ground Zero
http://www.pryormountains.org/welcome-to-the-pryors/
http://www.pryormountains.org/natural-history/geology-2/geology/
http://www.pryormountains.org/wp-content/uploads/2010/05/GeologyTour-Oct-2011-a-mobile.pdf