Euchee Creek Trails Outcrop Earthcache EarthCache

This cache is an EarthCache. In order to log this cache, you must answer the questions at the bottom with an e-mail to the cache owner. Failure to answer these questions will result in deletion of your log. The coordinates will take you to a sign with some information to get you started. You can complete this cache staying entirely on the trail and well worn paths. The park is only open during daylight hours.

Granite rock outcrops are a prominent feature of the Appalachian and Piedmont regions, and Georgia is full of them. It is estimated that more than 90 percent of the approximately 12,000 acres of exposed granite in the Southeast is located in Georgia², including Stone Mountain, the largest outcrop in the world¹. When you reach this geocache you are less than ten miles from Heggie's Rock, a protected National Natural Landmark and a flat granite rock outcrop that stands almost 70 feet above the surrounding forest. Heggie's Rock, however, harbors a couple endangered species, and is only open to the public on a limited basis³. Not exactly a place for trampling hordes of geocachers. Instead, we'll have to learn our lessons from the rock outcrop at Euchee Trails.

How did they get here?

Geologists estimate that most of the granitic rocks that outcrop in the Piedmont of the southeastern United States are approximately 300-350 million old. These outcrops were formed by the intrusion of molten granite into preexisting country rock at a depth of about sixteen kilometers below the surface. Over millions of years, erosion removed thousands of feet of overlying rock, exposing the more resistant bodies of granite.²

Granitic outcrops vary tremendously in size, shape, and position in the landscape. Some consist of small, flat-lying exposures (or flatrocks) only a few square feet in area. At the other extreme, Stone Mountain is a steeply sloping outcrop that covers nearly 600 acres and rises approximately 825 feet above the surrounding countryside.²

The Fall Line

This map shows Georgia's aquifers. The Fall Line is the line below the brown shaded region.

One of the contributing factors to the outcropping in this area is the proximity to the "fall line." The fall line cuts across Georgia from Augusta to Macon to Columbia and marks the transition from the Piedmont region to the Upper Coastal Plains region. The fall line generally marks the transition from crystalline rocks of the Piedmont to the sedimentary rocks of the coastal plains. For rivers that originate in the Piedmont, rock outcroppings result in rapids and waterfalls, hence the name "fall line."²

The worn-down rocks of the Piedmont region pass below the sedimentary rocks of the Atlantic Coastal Plain for more than 150 miles from the fall line. In the Piedmont, rocks are frequently covered by thick layers of decomposed rock known as saprolite. Saprolite is made up of clay minerals rich in silicon, aluminum, and some other elements, plus more or less pigmentary iron oxides (creating the famous red clays of Georgia) and resistant minerals such as quartz.² Rock outcroppings are those rocks which have emerged in areas where this layer of red clay has eroded away.

From rock to soil

Because of their harsh exposed environment, rock outcrops offer a good place to observe primary succession and early soil development. The first organisms that can survive on the bare rock surface are lichens and mosses. These organisms actually dissolve rock with weak acids. After many years, through chemical and physical decomposition, a thin soil layer is formed. Soil allows other tolerant plants to establish, such as Diamorpha and Sedum, both succulent plants (fleshy leaves that hold moisture) well designed to withstand long periods of dry weather. As the soil continues to thicken, Broomsedge, Sandworts, and Orange grass can colonize the rock. Confederate Daisy, an endangered and endemic species, is quick to follow. Eventually small shrubs and trees will entirely cover the rock outcrop. This entire progression from rock to forest can often be seen on a single rock outcrop transect starting on bare rock and walking towards the encroaching forest at the outcrops edge.¹

To summarize (and help a bit with the answers below), the stages of soil/plant development on rock outcroppings are:

1. Lichens
   
2. Moss
   
3. Annuals
   
4. Perennials
   
5. Shrubs
   
6. Trees
   

Sources

1. The New Georgia Encyclopedia articles "Granite Outcrops" "Fall Line" and "Piedmont."
   
2. The Georgia Department of Natural Resources.
   
3. Heggie's Rock | The Nature Conservancy
   

Required questions/actions

1. How large must an outcropping be to be represented on the sign?
   
2. Using the sign, how many rock outcroppings can you count in Columbia County (approximately)? How many in Richmond County? What things (from the reading above) might explain this difference?
   
3. "Measure" the nearby rock outcrop (the one with a smiley face) with something you have on you. What are its dimensions? (units can be shoes, arm lengths, etc.)
   
4. What stages of soil development can be observed on this rock?
   
5. Go to N 33° 27.494' W 082° 13.788' and observe the nearby rocks. Based on the information on soil erosion and erosion, and judging from other nearby outcroppings, does this outcropping appear to be natural? Why or why not?
   
6. Continue back along the trail to N 33° 27.392' W 082° 13.717'. You should find yourself at a much larger rock outcropping. Carefully observing the extent of the rock outcropping, what stages of soil development can you see here?
   
7. Follow the worn path to N 33° 27.367' W 082° 13.675'. With your back to the rock outcropping, what remarkable terrain feature is in front of you? What role do rock outcroppings and subterranean granite play in the development of this feature?
   
8. (optional) Include a picture of a large or interesting outcrop you've come across in the park while geocaching, with your GPSr in the picture showing the coordinates. Try to post a unique outcrop.