Introduction

One of the most distinctive aspects of the North Carolina natural setting is the shape of the land.  Topography helped shape the history of the state and even today it is common for people to distinguish between the Piedmont, Mountains or the coastal parts of the state when talking about politics or other events.  Thus, these land regions have become historical/cultural divisions as well but their fundamental basis lies in the nature of the land.

More specifically, these distinct and historically important sub-areas are: (1) the Appalachian Mountains of western North Carolina; (2) the Piedmont Plateau, a broad belt that cuts diagonally  across the middle of the state and; (3) the Coastal Plain, a low lying plain that comprises the eastern portion of North Carolina (Figure 1a).  The latter is often sub-divided into the Outer Coastal Plain, or Tidewater, section near the coast and the Inner Coastal Plain, farther inland and mostly removed from the direct influence of the ocean. 

As shown in Figure 1a, physical boundaries typically divide counties, However, for statistical purposes it is necessary to place counties in just one land region. This adjustment is displayed in Figure 1b.

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(1a is of the natural regions (2.1 in the book); 1b is the map on which the natural boundaries are made to fit county lines (Figure 1.1 in the book).

Grandfather Mountain in the Fall Hugh Morton's North Carolina © UNC Press, 2003	Geologic History Land Regions Coastal Plain The Piedmont Appalachian Mountains	Piedmont near Winston Salem Hugh Morton's North Carolina ©UNC Press, 2003
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The geologic processes that formed this landscape have operated over a span of at least 1.2 billion years and have involved massive shifts in the plates that make up the earth’s crust (Figure 2).  About one billion years ago the eastern margin of North America was situated where the Blue Ridge Mountains are today.  To the the east lay a wide ocean containing island arcs and micro-continents that were moving as the plates they rested on shifted.  Beginning about 450 million years ago, the island arcs and micro-continents began to collide with, and add on to, eastern North America.  These collisions generated heat and pressure that thrust the rocks up into great mountain ranges, often associated with the injection of molten magma into subterranean chambers and volcanic eruptions.

The last major mountain building event was the result of Africa colliding with North America about 300 million years ago.  The energy from this collision was so great that a mountain range the size of the present Himalays was built.  The effects of the collision can be seen in the folded rocks as far west as central Tennessee.  The eroded debris from those mountains built the widespread deposits of the Appalachian Plateau that extends across Kentucky as far west as Cincinnati. 

The supercontinent formed by the collision of North America and Africa is known as Pangea and it persisted for about 100 million years.  Pangea began to stretch apart about 225 million years ago and, by 200 million years ago, the Atlantic Ocean began to open.  With the opening of the Atlantic Ocean, the Coastal Plain began to form.  It is constructed mainly from the sediments that eroded from the nearby mountains and carried to the shore by rivers.  These sediments were deposited in alluvial, coastal and shallow marine environments as the ocean invaded far inland (Figure 3).  With time, these deposits built eastward, constructing an enormous wedge-shaped deposit of sediments and sedimentary rocks.  The top of the sedimentary wedge is nearly flat while the base of the wedge increases from zero thickness along its inland margin to more than 10,000 feet under Cape Hatteras.  Offshore, the wedge reaches a maximum thickness of 30,000 feet and begins to taper once more toward the ocean floor.  The rocks within the wedge dip gently eastward and progressively younger deposits can be seen on an eastward traverse across the Coastal Plain.

During the long interval of the construction of the sedimentary wedge, sea level fluctuated many times.  On occasion the shoreline was situated at least as far inland as the Fall Line (Figure 3).   At other times the shoreline was located farther east, at the edge of the continental shelf.  Some of these fluctuations in sea level are recorded by terraces on the Coastal Plain,  where the eroded edge of a terrace represents a temporary shoreline.  About 18,000 years ago, sea level dropped as much as 400 feet below its current level.  This drop was caused by the growth of continental glaciers in North America, Europe and Asia.  As the glaciers grew, they removed vast quantities of water from the world’s oceans.  With the end of the Ice Age, the glaciers have largely melted and returned pent-up waters to the oceans, causing sea level to rise once again.  Sea level continues to rise today at a rate of about six inches per century.

The current geology of the state is the result of these episodes of continental collisions, mountain building, fluctuations in sea level and erosion.  While this land may seem constant to the human observer, it is in fact a very dynamic situation that is changing constantly, albeit slowly.

The Coastal Plain

The Coastal Plain forms the eastern edge of North Carolina, making up about 45 percent of the state’s total land area.  It is bounded on the east by the Atlantic Ocean and on the west by the Fall Line, a broad zonewhere the soft rocks of the Coastal Plain meet the hard crystalline rocks of the Piedmont.  The Coastal Plain varies in width from 100 to 140 miles.  It rises gently in elevation to the west, from about sea level at the coast to as much as 500 feet in the Sand Hills district.

Wetlands are a dominant feature of the North Carolina Coastal Plain.  Wetlands are defined as “. . . those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions.”  That is, the descriptive characteristics of wetlands are their hydrology, hydric soils and wetland plants.  The fact is, however, that they are creations of topography that causes land areas to drain poorly, whether because of terraces left along ancient shorelines or due to flat lying deposits on flood plains.

Originally North Carolina had about 10.3 million acres of wetlands.  As Figure 4 shows, the vast majority of this acreage lies on the Coastal Plain.  Wetlands on the Piedmont or in the Mountains tend to lie along streams whereas those near the coast are products of that region’s low elevation.  About half of the state’s original wetlands have been drained and converted to forestry, agriculture or urban uses.  Most of the remaining inventory is in freshwater wetlands.  About 240,000 acres originally were in salt marshes and more than 85 percent of that acreage remains undisturbed.  Wetlands can provide valuable wildlife and aquatic life habitat, shoreline stabilization, and flood storage.  About two-thirds of North Carolina’s rare, threatened and endangered species of plants and animals live in wetlands.  Wetlands often provide crucial water quality benefits by trapping sediment, nutrients and toxic pollutants by filtering them from urban or agricultural runoff before they enter streams.

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In June, 1998, a Federal court temporarily lifted controls on wetland draining and conversion. Between then and March, 1999, about 12,000 acres were drained without permits. Since that time about 6,400 of those acres have been restored to their original condition. The NC Division of Water Quality resumed permitting with stricter application of the legal requirements in March, 1999. Table 1 summarizes the wetlands acreage that was permitted for drainage by the NC Division of Water Quality between 1992 and 2001. The large acreage on the Coastal Plain in 1997 was due largely to development of the Buckhorn Reservoir. The large removal in 1998 was attributable largely to the expansion of the Texas Gulf phosphate mine in Aurora. The sharp drop in acreage beginning in 1999 reflects the more rigorous enforcement by the NC Division of Water Quality.

The Coastal Plain is sub-divided into two major sub-areas.  The Outer Coastal Plain, or Tidewater, lies closest to the ocean, is extremely flat, averages less than 20 feet above sea level and contains large swamps and lakes indicative of poor drainage conditions.  Eleven of the 12 counties that have 55 percent or more of their areas in wetland soil areas are in the Tidewater section.  Streams on the Outer Coastal Plain are brackish and subject to tidal fluctuations in level.

The Fall Line marks the boundary between the Coastal Plain and the Piedmont.  Rivers that rise in the Blue Ridge Mountains flow across the Piedmont and enter the Coastal Plain at the Fall Line.  This boundary is characterized by steep river gradients and rapids. Downstream of the Fall Line, the rivers flow to the southeast and have carved broad, low valleys in the soft, easily eroded sediments of the Coastal Plain.  There the rivers have gentle gradients and are flanked by swamps and marshes.  They are generally navigable all the way up to the Fall Line, an important factor in the early settlement of the region from the coast.  A distinctive feature along the Fall Line is the Sand Hills (Figure 1).  These deposits originally formed as wind-blown sand dunes.  They are permeable, quartz-rich deposits that produce well-drained, acidic soils that are deficient in plant nutrients.

The coastal margin north of Cape Lookout is a “drowned coast,” in which  the sea level rise associated with the end of the last Ice Age and the continual melting of the ice caps has caused the ocean to invade the lower reaches of river valleys. This drowning has produced large embayments such as Albemarle and Pamlico Sounds.  Associated with these embayments is a string of barrier islands that are separated from the mainland by as much as 20 miles, the Outer Banks(Figure 5).  These linear islands apparently were formed as sea level rose over old  beach ridges and sand dunes.  Continued rises in sea level, accompanied by wave and wind action, cause these islands and their lagoons to slowly move inland.  This steady inland migration, known as barrier island rollover, plus the exposure to hurricanes and other storms, makes the many developments along these attractive shores highly vulnerable to damage and destruction.  The most famous example of this is the historic Cape Hatteras lighthouse. This lighthouse has been moved farther inland to protect it from erosion.

The lagoons and sea marshes along the coast near the Outer Banks are vital parts of the coastal ecosystem.  The shallow shoals and sand bars that are associated with barrier islands are constantly shifting in location.  They have presented sailors with very hazardous waters in which to navigate and this stretch of the Atlantic coast is so littered with shipwrecks that it is known as “The Graveyard of the Atlantic.”  These dangerous waters also made it difficult for early explorers and settlers to land on the northeast coast of North Carolina.

South of Cape Lookout is the Cape Fear Uplift, where the coast was gently folded upwards.  Instead of drowning the river valleys, the uplift exposed an even coastline, along which have formed long stretches of broad beaches.  The deep embayments found to the north are not present, nor are extensive barrier islands.  Historically, this length of coast was somewhat more accessible, despite the Frying Pan Shoals that make the mouth of the Cape Fear River, the entrance to the port of Wilmington, dangerous and which requires dredging to maintain a navigable channel.   Today this region is known for its miles of wide, sandy beaches that extend southward through the Grand Strand of South Carolina.

The Piedmont

West of the Fall Line is a geologically ancient region that is underlain by a complex of metamorphic and igneous rocks .  The rocks are remnants of the previously mentioned  major mountain system that was created over 300 million years.  The associated upheaval involved volcanic activity as well as the folding and faulting of the pre-existing rocks.   After the uplift was over, erosion took hold and wore away the mountain chain, leaving the contemporary, rolling plateau of the Piedmont.  Here and there areas of more resistant rocks form hills or low mountains on the surface of the Piedmont.  These hills are known as Monadnocks.  Examples are the Uwharries, Sauratown Mountains, Kings Mountain, the Brushy Mountains and South Mountains.  In other areas, such as the Carolina Slate Belt, somewhat softer rocks have eroded more deeply, forming lower areas that are often filled by lakes.

The Piedmont covers about the same amount of area as the Coastal Plain but it is higher in elevation, ranging from as low as 300 feet at the Fall Line to as much as 1,500 feet at the foot of the Blue Ridge Mountains.  Seven major rivers and their tributaries (Dan, Tar, Neuse, Cape Fear, Yadkin, Catawba and Broad) drain the eastern flanks of the Blue Ridge, carving narrow, deep valleys in the hard rocks of the Piedmont.  These streams and their valleys are not navigable but they have afforded numerous sites for waterpower uses.

The record of the early stretching of Pangea is seen where the crust of the Piedmont fractured and great blocks subsided (Figure 6).  These long lowlands, mainly along the southeastern edge of the Piedmont, are known as Triassic Basins and they include the Durham, Sanford and Wadesboro Basins. Rivers filled these valleys with sediments from the adjacent land.  Some iron ore deposits formed in them and these were important during colonial times but they are too no longer of economic interest today.  Swampy conditions within the basins led to the accumulation of small coal deposits which also were of some value during the colonial era.

Some of the Piedmont rocks contain gold and other valuable metals and the area from Cabarrus County south into Georgia was the site of the first U.S. gold rush.  The area supplied most of the U.S. gold production from its discovery in 1799 until the California gold rush of 1849.  Mines were operating within the City of Charlotte into the early twentieth century and some other Piedmont mines were worked into the 1930s.

Topographically, the Piedmont forms a wide, rolling plateau between the low relief Coastal Plain, to the east, and the more rugged mountains to the west.  Historically, the Piedmont has been easier to cross than either of the other landform regions and, until recently, most major transportation routes followed it.  Thus, the Piedmont has acted as a natural corridor between the northeastern U.S. and the Deep South, from the time of American Indians until today.  Early colonial trails followed Indian paths, then came the North Carolina Railroad and later highway I-85.  All followed the natural corridor that was created by events that began millions of years ago. 

Appalachian Mountains

The Piedmont ends and the Appalachian Mountains begin abruptly at a major fault line, the Brevard Fault, west of which rises a steep escarpment, the edge of the Blue Ridge mountains.  That escarpment rises as much as 1,500 feet above the adjacent land, clearly visible at places such as where I-77 crosses into Virginia and rises quickly to pass through Fancy Gap in the Blue Ridge Mountains.  It is visible also in the Swannanoa Gap, where I-40 crosses the Blue Ridge mountains and enters into the Asheville Basin.  The Blue Ridge Mountains form the eastern continental divide, with waters draining off its western slopes into the Mississippi River system and those from the eastern slopes flowing into the Atlantic Ocean.  Rivers that originate, at least in part,  on the eastern flanks of the Blue Ridge in North Carolina include the Roanoke, Yadkin, Catawba, Broad and Savannah Rivers.  The major westward flowing rivers are the New, French Broad, Little Tennessee and Hiawassee.  The New River, despite its name, is very old, as indicated by the fact that its winding course has maintained itself despite flowing across hills and valleys.  It is believed that this happened because at one time the river flowed over a plain that developed into mountains as the land was uplifted and erosion wore away the soft rocks faster than the harder ones.  The strong flow of the New cut through both hard and soft rocks, thus maintaining its original valley. 

The Appalachian mountain system reaches its greatest width and elevation in North Carolina.  The Blue Ridge Mountains are the eastern edge of a highly dissected mountain plateau.  This plateau is bounded on the west by the Unaka and Great Smoky Mountains, along the Tennessee border.  In between are a number of cross ridges and broad intermontane valleys.  Most prominent of these cross ridges are the Black Mountains, which include Mount Mitchell, at 6,684 feet the highest peak in the eastern United States.  Other cross ridges are the Pisgah, New Found, Balsam, Cowee, Nantahala, Snowbird and the Valley River Mountains.  Altogether, in North Carolina there are 43 peaks that exceed 6,000 feet in elevation and another 82 that range between 5,000 and 6,000 feet.

The mountains of North Carolina are made up of a variety of rock types but the predominant type is a mass of metamorphic rocks.  Metamorphic rocks (Greek for “changed form”) are pre-existing rocks of any type that have been changed by heat and pressure but not so much that their original character is not discernible.  Limestone became marble, for example.  Usually the result was to create a rock that is  relatively resistant to erosion.  Associated with metamorphism has been faulting and the intrusion of molten (igneous) rocks into the area.  Rocks in the mountains range in age from over one billion years to about 400 million years.  The western part of the mountains contain the oldest rocks in North Carolina and they are separated from slightly younger rocks in the eastern mountains by several fault zones.  The older rocks are referred to as basementrocks.  They were mostly igneous in origin, prior to metamorphism, and they comprise a remnant of the original mass of ancient North America.

In the eastern mountains the rocks are somewhat younger mixed volcanic and sedimentary rocks that were deposited on the continental margin and subsequently metamorphosed during the episodes of mountain building.  These rocks make up the main mass of features such as Mount Rogers and Grandfather mountain.  Intermontane basins, especially the Asheville Basin, at the confluence of the French Broad and Swannanoa Rivers, have provided most of the level land on which people have settled in this region.