Independence Rock - 6/11/14

Independence Rock

Independence Rock is a stock feature, meaning that it is an igneous mass that was formed underground, but is smaller than a batholith. However, it can become one if it becomes more exposed above the surface. It was formed along normal faults meaning the hanging wall moves down from tensional stress. 

On a historical level it is one of the features on the Oregon trail. It was also a landmark used for cavalry and landrushers in 1849 and a check point for the Pony Express.  Many people have inscribed their names into the rock (and surprisingly it proves boys once had nice handwriting) and wagon ruts can often be found near it.

Other features found on the rock include coarse-grained mineral veins. The veins found throughout the rock are made up of quartz. These quartz veins are formed when hydrothermal fluids, or hot water solution, runs through the rock.

The uplift of the rock results in erosion of overlying rock, which causes a decrease in pressure and the rock to expand and fracture. Next, Independence Rock began exfoliating along sheet joints. The granite of Independence Rock weathers in blocks that then round out. This process is called spheroidal weathering.

Also of note, Independence Rock is an exfoliation dome, meaning it is a large dome shaped rock formed by exfoliation. Exfoliation is a process that includes the removal of concentric layers of rock along sheet sheets.

In terms of mineralogy and rock properties, the rock is made up of a typical granite composition, with a bit of a unique property. While it still has typical "Orthoclase - Quartz - Hornblende" composition, it is unique in that parts of the rock actually have a porphyritic phaneritic texture. This proves that this rock began the cooling process underground. The crystals that were much larger cooled at a much higher temperature, for a longer period of time, whereas the smaller crystals cooled much quicker at lower temperatures as the magma moved closer to the surface.

Overall, I would say that exploring Independence Rock was a pretty incredible experience. It was a challenge to climb up, and many of us felt the 3700 ft. elevation difference, compared to Rochester, NY, while climbing it. Once on top though, the view was astonishing. 

Thanks for reading! For more pictures from this trip, feel free to visit Brandon's Tumblr page at: 

http://www.tumblr.com/blogs/Yellowstone-Adventures

Cheers!

Cindy & Brandon