Welcome to the ancient Roan Highlands, home to some of the oldest rocks in the ancient Appalachian Mountains. GPS coverage is still spotty up in the mountains, but luckily you're going to be visiting the beautiful Gristmill visitor center "at the bottom of the hill". Here you will find a couple of very interesting displays inside which detail both the historical and geological background of the Roan Mountain area. The visitor center may be small, but it teaches a lot and has some nice trails nearby to some other interesting sites. You should have no trouble finding the displays once inside the visitor center.
** Update on Accessibility **
I have spoken to a ranger at the Grist Mill visitor center and he has informed me that there is a side entrance to the museum area which is ADA wheelchair accessible. Terrain has been updated to reflect this.
(Image courtesy of... Well... Me, actually.)
Visitor Center Coordinates (For those of you that want to do it old school)
36°10.5740'N
82°4.7480'W
Physical Address (For those of you that prefer the easy route)
Gristmill Visitor Center
527 TN-143, Roan Mountain, TN 37687
Hours of Operation:
8 am - 4:00 pm
7 days a week
If your smart, you will call ahead to make sure they are open before getting up into the hills. It gets cold up here during winter and ice / snow storms can make travel just about suicidal at times. So play it safe no matter the weather and give them a quick call at (423) 547-3906 to make sure they are operating. Alright, now that you've been briefed, let's get down to business.
Overview
This part of the country has seen a LOT over its lifetime. Supercontinents and mountain chains have come and gone. Some of these mountains may once have rivaled the current Himalayans, but eventually time catches up to them all and the current Appalachians are no exception. At other times, this area may have actually been underwater in a shallow sea. This geological display, which has been provided by the Roan Mountain State Park system, details how these ancient mountains came to be, how old some of the rocks are, and (perhaps best of all) the chance to touch multiple pieces of truly ancient geology. Yeah, that's right, for once you are actually ENCOURAGED to touch the displays! One of these rocks you'll have the chance to handle is far older than the rest and possibly could have been a part of another continent at one time (Moecher, D. P., Et. Al. (2020)), but I can't give everything away here. If you want to claim this EC, you've got some reading to do and some rocks to play with.
Background
Formation of the mountains
Land masses are constantly being pushed, shoved, split, and crushed at earth's surface. This action, which is known as plate tectonics, forced layers of the earth's crust up into what are today's Appalachian mountains. The Appalachian mountains are a classic example of the opening and closing of an ocean basin and the collision of continents, based on the theory of plate tectonics.
Plate tectonic theory was developed in the 1960s by combining the continental drift theory (originally created by the German Meteorologist Alfred Wegener) and convection currents of partially molten rock below the plates. The theory states that the earth's surface is made up of separate rigid plates that move about and carry the continents and ocean floor along with them. They rift apart, slide past each other, and sometimes collide into each other creating earthquakes, episodes of mountain building, and volcanic activity.
The current day Appalachian mountains were the result of the collision of the North American and African continents, which helped form the super continent Pangea. In the Roan Mountain region, thrust faulting brought deep slices of the continental bedrock towards the surface. Because older rocks were brought to the top of the pile and millions of years of erosion have exposed them at last, some of the typically deeper (and older) portions of the crust can be seen on the surface today. However, the forces that created this mountain chain ended over 200 million years ago and since that time erosion has taken its toll on these once lofty peaks. One day, perhaps, these mountains will be reduced to nothing more than a flat plain until the next continental collision occurs and new mountains are born once again.
Formation of the rocks
The rocks in this area are primarily igneous and metamorphic. The metamorphic rocks were formed by the action of heat, pressure and chemical changes when the rocks were deeply buried and earth's crust began to shift. The igneous types are plutonic meaning they solidified from melted rock below the earth's surface. The hardening of melted rock (magma) via solidification and crystallization forms different types of igneous rocks. As it nears the surface, some will solidify underground while some may break through to the surface as volcanoes. None of the igneous rocks in the RMSP are volcanic however. The two main types of igneous rock in this area are gabbro and granite which are formed from magmas that had very different chemical compositions and formed at different time periods. The difference in chemical compositions likely indicates that different geological processes were at work when the magmas rose towards the surface, such as continental collision or continental rifting. Closely examining the chemical composition and current state of the rocks (Igneous, Metamorphic, or Sedimentary), can help write a story for the land surrounding those rocks.
Chase the smiley
Once inside the visitor center, hang an immediate right and you should see the display on the wall to your right. Best of all, it has 8 rock samples sitting at the bottom for you to play with. As with most earthcaches, please don't post the answers in your log, send them via E-mail. I have been told, by a park ranger at the site, that the side entrance allows entry without stairs to the display area if needed.
Logging Requirements
After reading everything over, playing with the rocks, and summoning your inner Geologist, answer the following questions:
1. The Silhouettes of 3 different mountain ranges are displayed. Which mountain range do you think is the oldest?
2. We know that two different types of magmas with unique characteristics formed the Bakersville Gabbro and the Beech Granite. Which one do you think is most likely reponsible for the iron deposits in the area?
3. Find the Bakersville Gabbro and the Beech Granite samples below the display. Do you notice any significant color differences in them?
4. Compare the 2 rock samples you can lift (Augilite Epidote & Magnetite). Which rock do you think is heaviest?
5. Do you think there might be some specific element in your choice that makes it weigh more? If so, what?
If you're still feeling froggy after all that hard work, feel free to post a picture of your favorite rock from the line up. All I ask is that you don't include any answers in your photos.
Alright, now you might be more enlightened, but wouldn't you like to see some of these pretties out in the wild? Let me go ahead and answer that for you. YES, you would. So, if the weather is nice, then by all means hike the short trail near the visitor's center and go see the old mine entrance. Its a lovely walk in the woods especially in the fall when the leaves are changing. Then, when you're ready to see one of the most beautiful places on earth, drive on up the road to Carver's gap and hike the roughly 30 minutes ( roughly 1 mile) up to Round Bald. If you have any questions, just ask someone at the visitor's center and remember to take a jacket with you even in the summer. Personally, It's one of my favorite places on this little blue marble and the views are amazing (especially at sunset). Keep in mind those rock samples you interacted with at the visitor's center as well. Your going to see some of them on your hike up to the top.
Special thanks go to the Roan Mountain park service for letting me place this Earthcache and for all their hard work maintaining such an awesome park / geology display in the first place.
Special thanks also goes to Geoshrooom of course. She puts up with my 12 hour road trips all over the Southeast and typically manages to hide the stark terror in her heart when were "off the grid", sort of speak. Luckily, this EC just required the long car ride and a Tacobell that somehow ran out of chicken.
References
Moecher, D. P., Harris, F. C., Larkin, E. A., Quinn, R. J., Walsh, K. B., Loughry, D. F., Anderson, E. D., Samson, S. D., Satkoski, A. M., & Tohver, E. (2020, October). Zircon U-Pb geochronology and Nd-Pb isotope geochemistry of Blue Ridge basement in the eastern Great Smoky Mountains, U.S.A.: Implications for the Proterozoic tectonic evolution of the southeastern Laurentian margin. American Journal of Science. https://doi.org/10.2475/10.2020.02