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Black Rock Mountain State Park
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Black Rock Mountain is part of the Blue Ridge Mountains and is Georgia’s highest recreation area – with the summit of Black Rock Mountain reaching an elevation of 3640 feet.  This area has a wide variety of ecosystems – some that prefer cool, moist conditions and others that like dry, sunny environments, some that you will find on the high ridgetops and others that are common on the lower slopes.  This is a great place to see the five layers of the forest – the canopy, understory, shrubs layer, herb layer, ground layer.  You will walk through a hardwood forest that is in a near-climax stage in its life cycle.  Unless there is a catastrophic event, such as a fire or wind or ice storm, the forest will become stable.  You will also see old logs in the process of decomposing and creating nutrients for new forest growth.

This area was logged until the early 1900s, but you will see White Oaks that have grown to between 60 and 80 feet tall.  You will also find young American Chestnuts.  Once the dominant tree in this area, they were extensively logged for their valuable lumber.  Around 1904, though, a fungus bark disease was introduced from Asia into the New York City area.  This spread through the chestnut population and within 40 years had virtually eliminated the tree.  The chestnut blight is still present today and young chestnuts rarely grow very large before they, too, are killed by the disease.

You will see a large boulderfield, caused by a climate-related phenomenon during the Pleistocene period.  During the ice age that ended about 10,000 years ago, the Southern Appalachians experienced long, harsh winters with significant ice and snow.  During this time, water seeped into the rocky crevasses and repeatedly froze and expanded.  This eventually pried loose rocks from the face of the cliff where they rolled down the mountain slope.  In the southern mountains, these boulderfields usually occur above 3,000 feet and only in very moist, north-facing coves. 

Rabun County has three major rivers – the Tallulah, the Little Tennessee, and the Chattooga.  On the summit of Black Rock Mountain is the only place where all three watersheds come together.  Rainfall that drains northward off the summit goes into the Little Tennessee; water running toward the south and the east flows to the Chattooga; and runoff from the westward slope enters the Tallulah.  The ridge that you will hike on forms a section of the Eastern Continental Divide.  This separates the watersheds of rivers that flow eastward to the Atlantic and those that flow westward to the Gulf of Mexico.  On Black Rock Mountain, water that drains off the right of the trail will go southward into the Chattooga, then the Tugalo, and eventually the Savannah River which empties into the Atlantic.  Water draining off the left side of the trail takes a far longer route, but eventually finds the Mississippi River and empties into the Gulf of Mexico.

The Blue Ridge Mountains, including Black Rock Mountain, were originally formed when the continental plates of Africa and North America collided 250 million years ago.  The ancestral Blue Ridge was uplifted and some layers of rock became so hot they melted, then cooled to form granite.  Other layers of rock were subjected to intense heat and pressure and different types of shists and gneisses formed.  Black Rock Mountain is primarily made up of biotite gneiss – the dark color of the mineral biotite gave the parks “Black Rock” outcrop its name. 

The Blue Ridge Mountains were thousands of feet higher than they are today and the rocks you now see were once far below the Earth’s surface.  Continuous erosion has exposed the outcrops you see today.  The rounded look of the Blue Ridge Mountains, and other ranges of the Appalachians, are due to the fact that they are some of the oldest mountains in the world and long periods of erosion have left smooth mountains.