You are standing in a very special place….
On the Boulder Batholith, which at this point is also on the Continental Divide or Great Divide and on Homestake Pass.
A batholith (from Greek bathos, depth + lithos, rock) is a large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite, quartz monzonite, or diorite. A batholith is an exposed area of (mostly) continuous plutonic rock that covers an area larger than 100 square kilometers.
The Boulder Batholith was named for the prominent rounded boulders that typify its landscape, the result of spheroidal weathering of fractured granite. It lies roughly between Butte and Helena, and between the Deer Lodge (Upper Clark Fork) Valley and the Broadwater (Upper Missouri) Valley. The volcanic Elkhorn Mountains are a large mass of forested lava associated with the batholith. Regional uplift brought the deep-seated granite to the surface, where erosion exposed the rocks and the extremely rich mineral veins they contained. Hundreds of millions of dollars of copper, silver, gold, zinc, lead, and other metals have been mined from the batholith, both using underground mining and pit mining. This area has a rich and colorful history of mining. Butte has many educational and informative opportunities to learn about the mining history if you have an interest in learning more.
To claim this Earthcache you will have to answer the following questions and email me (firstname.lastname@example.org) the answers. Please do not post answers in your log. If answers are posted, your log could be deleted without warning. You are invited to post a photo if you can. Thanks!
1. How many separate bodies formed from the individual pulses of rising magma?
2. What causes the smooth boulders you see?
3. What were the two end results of the magma that flowed to create the batholith?
4. What crystals are contained in this granite?
5. According to the diagram on the information sign, are you currently located in an area where the granite is light or dark?