✔️ Important Stuff!
This is an Earthcache-- this means that there is no physical container. To be able to log this as a find, you must complete the tasks below (Including the photo).
The Earthcache is located in Cherokee Bluffs Park. The cache is NOT 24/7. Hours vary by season, but dawn-to-dusk is a good general starting point. Please be sure to follow all park rules.
❓ Why are you here?
When you arrive at the posted coords, you will notice a bunch of "white stuff" on the rocks. You're here to learn about that!
🥾 Logging Requirements
To claim a find for this Earthcache, please post your photo with your log and send your answers to the three questions below via geocaching message or email. Do not post the answers in your public log. You may log your find immediately after sending your answers.
Photo (Required): Post a photo of yourself, your GPS, or a personal item with some of the lichen (You'll learn about that below!) in the photo. Note the photo is required and logs without a photo will be deleted. You do not have to have your face in the photo, but you must have something personally identifiable visible.
Question 1: Look closely at the edges where the white lichen meets the bare, uncovered rock. Does the rock surface directly underneath or right at the edge of the lichen feel smooth and solid, or does it feel rougher and more crumbly than the completely bare rock?
Question2 : Are the white lichens growing more heavily on the exposed, sunlit faces of the rock, or deep inside the dark, shaded crevices? Why do you think they prefer that environment?
Question 3: Based on the geological lesson above, explain how the white lichen acts as both a chemical and a mechanical force of erosion on this specific outcropping.
📌 About Cherokee Bluffs
(Note: this introduction section is repeated in each of the Earthcaches hidden here. Feel free to skip if you are doing multiple EC's...)
Cherokee Bluffs Park in Flowery Branch, GA, features natural granite rock outcrops and cliff overhangs formed from the Piedmont region's crystalline bedrock. These formations sit atop rolling hills, providing distinct topographical features alongside historical significance. As you walk beneath the massive overhanging rock shelters here (locally known as "Stone Mountain's Toenails"), look closely at the walls of the cliff face.
Key Geological Features
- Granitic Outcrops: The main feature of the bluffs is a massive granite and gneiss outcropping that emerges along the ridge. Sometimes locally compared to Stone Mountain's geology, these formations are composed of minerals such as quartz and feldspar.
- Origin and Age: Like many geological units in Hall County, the underlying rock is part of the Piedmont Province. It formed during the Paleozoic Era when magma solidified several miles beneath the Earth's surface before tectonic uplift and erosion brought the rock to the surface.
📌 Geology Introduction
Welcome to Cherokee Bluffs Park! As you hike along the trails and marvel at the massive granite outcroppings (locally nicknamed "Stone Mountain's Toenails"), it’s easy to think of these rocks as completely permanent features of the landscape. However, a quiet, slow-motion battle is taking place right on the surface of the stone.
If you look closely at the rock face at this location, you will notice large patches of a crusty, ash-white substance coating the granite. This isn't just a stain or a mineral deposit—it is a living organism actively reshaping the geology of the park through biological weathering.
📖 The Geological Lesson: Biological Weathering & Lichen
Weathering is the process that breaks down solid rock into soil and sediment. While we often think of wind and rain doing this work, living organisms play a massive role. This is known as biological weathering.
What is the white stuff?
The white patches dominating these rocks are Lichens (specifically crustose lichens, which grow tightly pressed against the rock surface like a crust). A lichen isn't a single plant; it is a symbiotic partnership between a fungus and an alga.
How do they destroy granite?
Lichens attack the hard granite using two simultaneous methods:
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Chemical Biological Weathering (Lichen Acids): Lichens produce specialized organic compounds known as "lichen acids." As these acids seep into the rock, they chemically react with the minerals that make up the granite (like feldspar and mica). The acids dissolve and leach out these vital minerals, weakening the crystalline structure of the stone and turning hard rock into a soft, crumbly powder over time.
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Mechanical Biological Weathering (Micro-Fracturing): Lichens have tiny, root-like anchors called rhizines. These anchors wedge themselves into microscopic pores and cracks in the granite. When the lichen gets wet from rain, it swells up; when it dries out, it contracts. This constant expanding and contracting exerts microscopic physical pressure inside the rock cracks, eventually flaking off tiny grains of quartz and mineral crystals.
Through this teamwork of chemistry and physics, the white lichen slowly but surely disintegrates solid granite, creating the very first layers of new soil!