Geologists tend to think in textbook terms. Words like sinks and cauldrons, spoons, rifts and faults have a special meaning to those who understand the science. This article, however, is written for the laymen among us who want to understand the earth beneath our feet. The lay of the land in North Georgia changes dramatically from north to south as the Appalachian Mountains erode into the southern foothills. When people say "old as the hills", these are the hills they are talking about.
Georgia's northeastern climes were formed hundreds of millions years ago, long before their western cousins the Rockies. Known as the Blue Ridge Mountains, the escarpment that forms the eastern rim is volcanic, but has been dormant for eons. The peaks themselves are comprised of schist, gneiss and granite covered by oak and hickory thanks to the moist slopes that form the watershed for Georgia's major rivers.
Rock that forms the mountains erodes into these rivers, which is dutifully carried to the Piedmont and beyond, creating much of what is now south Georgia and Alabama. Less than two million years ago trees began to take root in the little bit of soil that remained on the mountains. Fed on the water the trees grew, holding more of the precious earth with their roots and a balance formed, the 40+ inches of rain sustaining the trees which now held the dirt. Even after 2 million years of work the trees have only managed to create about five inches of topsoil across these mountains. These are Georgia's tallest peaks, including Brasstown Bald at 4,784 feet, the state highpoint.
Based on changes in rock type, which geologists refer to as "boundaries", the Blue Ridge extend south to a line just south of Helen, Daholonega, Dawsonville and Canton. These mountains are characterized by rugged peaks, long ridges and dendritic hydrology (a fancy way of saying many small streams that become larger rivers). Rocks in the Blue Ridge are mostly metamorphic. Some of these rocks come from sedimentary rock, others from igneous rock such as the Corbin Metagranite (Canton), Salem Church Massif (Jasper), or the Fort Mountain uplift (Chatsworth), all first identified in the early 20th century. These rocks occasionally contain plutons from later seismic events and mark the western edge of the rock type boundary.
Just west of the McCaysville Basin are the Cohutta Mountains. Taken from Cherokee language, the word Cohutta means "poles of the shed," referring to the mountains ("poles") that hold the sky (roof of the "shed"). While most people, and many cartographers, consider them to be part of the Blue Ridge, they are geologically distinct from their eastern neighbor and actually form the end of the Smoky Mountains on the Tennessee-North Carolina border. Highway 411 in Murray County follows the western end of this chain. Further south the highway skirts the western edge of the Cherokee Uplands, a rugged set of smaller mountains that form much of the watershed for the Ellijay and Cartecay Rivers.
Using the belt Fort Mountain Gneiss as the western border the Cohutta Mountains stretch east towards the city of Blue Ridge. They are not as rugged as the Blue Ridge Mountains and have lower peaks because they were formed much earlier than the Blue Ridge. The underlying rock is identified as part of the Great Smokey Group.
The Brevard Fault Line follows the high ridge of the Blue Ridge and continues on towards Marietta where it shoots off to the west, leaving the state at the Alabama border close to I-20. I-575 and Ga. 515 closely parallel the fault line. Most of the area containing this line is known as the Hightower-Jasper Ridges which begins in the northeast corner of White County. A spur begins in Tennessee and enters Georgia under the city of McCaysville, a narrow area that runs through the McCaysville Basin separating the Blue Ridge from the Cohuttas. In the Y formed by the spur lies the Dahlonega Uplands, sometimes called the Dahlonega Plateau. This broad, high plain features gently rolling hills in the shadow of some of Georgia's highest peaks, and forms the Etowah River Basin.
The McCaysville Basin is an unusual feature of the state. The large, bowl-like shape in central north Georgia holds mineral riches that were not fully exploited until just before The Civil War. This is a geologically diverse region that has attracted miners for more than 100 years.
From the floor of the Great Valley to Fort Mountain State Park is a 2,000 foot climb, largest in the state. The Great Valley is a vast expanse west of the Cohuttas. This is the start of the Valley and Ridge (or Ridge and Valley) section of the Appalachian Mountains. Here long, wide valleys separate ridges. Much of the area was underwater until recently, in geological terms. To witness the valley floor to mountaintop, head east on State Road 52 out of Chatsworth, Georgia, to Fort Mountain State Park. An incredible change occurs. In slightly more than 5 miles the road climbs 2,000 feet with an accompanying change in flora and fauna. Nowhere else in Georgia can such a dramatic change be witnessed in such a short distance.
Three distinct regions can be found in extreme Northwest Georgia and are considered, with the Great Valley to be part of the Cumberland Plateau. The ridges of Lookout Mountain, its offshoot Pigeon Mountain and Sand Mountain, make up the Lookout Mountain district. The second region is known as the Chickamauga Valley and the third is the Armuchee Ridges.
In northwest Georgia the Great Valley gives way to ridges in a pattern that is repeated to the western corner of the state. Taylor Ridge, Rocky Face and Lavender Mountain are some of the better-known peaks that make up the Armuchee Ridges. Between these ridges and Lookout Mountain lies the Chickamauga Valley, which forms the watershed of Chickamauga Creek. In the northwestern corner the ridges widen, forming long plateaus that rise dramatically above the land below. Sand and Lookout Mountain begin in Alabama, running northeast, ending fifty miles later in Tennessee, bisecting northwest Georgia in between. Forming McLemore Cove, Pigeon Mountain forms like a thumb of Lookout Mountain. Here are the northernmost watersheds of the (western) Chattooga River and Chickamauga Creek. This region is known as the Lookout Mountain District.
South of the Blue Ridge Mountains lies the Etowah River Basin. This long, wide, fertile valley was home to Cherokee Indians, and the Creek Indians before them. The river, which General William Tecumseh Sherman called "The Rubicon of Georgia" flows in the southern half of the Jasper-Hightower Ridges.
East of this basin is a deep valley carved by the mighty Chattahoochee River. Part of and wholly contained in a larger geophysical feature called the Gainesville Ridges the river bisects the state from northeast to southwest. This valley and the surrounding hills were home to America's First Gold Rush. The Chestatee and the Yahoola, in the heartland of the Georgia Gold Rush, are tributaries of the Chattahoochee.
Between the Gainesville and Hightower-Jasper Ridges lie the Central Uplands, a belt of high plains that runs northeast to southwest, widening as it approaches the southwest. The gradual slope to the southeast created easily accessible waterpower for the early grist and cotton mills that provided most of the industrial employment in early North Georgia. Nearly all of Cobb County is encompassed by this feature.
Two massive eastern slopes form the shield across the southeastern Piedmont. The Winder Slope, which comprises the northern portion of the shield, is characterized by rolling hills and valleys, with a gradual slope to the southeast. Mostly igneous rocks, like granite combine with schists, amphibolites and gniess to form the underpinning of the Piedmont, with occasional faulting (Pine Mountain near Warm Springs, for example) and plutons (Stone Mountain). Geologically similar is the Washington Slope, which is flatter, with an even more gradual slope to the southeast.
Although the Brevard Fault Line is the best known and most active in Georgia, there are a number of others. The Soque River Fault follows (and created) the bed of the Soque River in Northeast Georgia. Running north from Cartersville the Carterville Fault passes just west of the massive containment of the Coosawattee River known as Carter's Lake. Mistakenly called the Carter's Dam Fault, it is more correctly titled thee Cartersvlle-Great Smoky Fault.
The northern end of the Talladega Fault line is known as the Emerson Fault, running from the Alabama state line to Emerson, Georgia. This line was once thought to join the Carterville Fault Line. The Salacoa Creek fault, in northwest Cherokee County may also be part of this grouping. The Springdale Church Faultline
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