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THE GEOLOGIC STORY OF THE OCOEE RIVER
U.S. Geological Survey General Interest Publication

Cover of 'The Geologic Story of the Ocoee River'

[Click on image for a larger view]

      Over millions of years, the Ocoee River has cut a steep, winding channel into a mountainside of hard rock. As you travel through the Ocoee River Gorge along US Highway 64 in the scenic Cherokee National Forest of southeastern Tennessee, take some time to look at the rocks along the way.

U.S. DEPARTMENT OF THE INTERIOR
U.S. Geological Survey

U.S. DEPARTMENT OF AGRICULTURE
Forest Service

TENNESSEE VALLEY AUTHORITY



Introduction
The Geologic Story
Maps
Folds and Faults
The Ocoee River
Mining at Ducktown
Weathering of Pyrite
More Information

Introduction

This web page showcases a brochure that tells the geologic story of the rocks exposed along the Ocoee River in Polk County, east Tennessee. The brochure was prepared by the USGS, in cooperation with Forest Service and Tennessee Valley Authority (TVA), to highlight the geology along a popular stretch of the Ocoee River.

As the Nation's largest earth-science agency, the U.S. Geological Survey (USGS) collects, analyzes, interprets, and distributes information on mineral, land, and water resources to all levels of government, educators, private industry, and the public.

The USGS works closely with the Forest Service to provide geologic and resource information for land-use planning by conducting mineral-resource assessments and other studies. The Forest Service oversees much of the land in Polk County, including the Cherokee National Forest.

TVA produces maps in cooperation with the USGS. TVA operates three dams on the lower Ocoee River to produce hydroelectric power and manages the flow of water in the river.

The Ocoee River area attracts thousands of visitors every year and includes the Ocoee Whitewater Center in the Cherokee National Forest, site of the 1996 Olympic Canoe/Kayak Slalom competition.

Image of kayaker on the Ocoee River
Kayaking on the Ocoee. [Photograph by Carter Hearn]

US Highway 64 follows the Ocoee River through the gorge, east of the town of Cleveland, Tennessee. Many interesting rocks can be seen from the highway in roadcuts and in the river bed starting near Ocoee Dam No. 1 (Parksville Dam). East of Ocoee Dam No. 3, the Ocoee River turns south and Highway 64 continues east to Ducktown.

As you read the geologic story, follow the map map icon and photo map icon icons to see some of the geologic features along the Ocoee River. The map will open in a new window.

The Geologic Story

The Earth is about 4.5 billion (4,500,000,000) years old. Over long periods of time, ancient continents have moved great distances, oceans have formed and later disappeared, and mountains have risen and worn away. Geologists read the history of the Earth, in part, by studying the rocks at the surface. Present-day locations of different types of rocks, and the minerals, textures, and structures (faults and folds) within rock units, are largely the result of plate tectonics - the formation, movement, and collision of plates (continent-size, rigid slabs of solid rock). Here is a glimpse of part of the geologic story revealed by rocks in the southeastern United States:

750 to 570 million years ago (during the Late Proterozoic Era)

Chart showing the Ocoee River during the Late Proterozoic Era 750-570 million years ago
750 to 570 million years ago

570 to 240 million years ago (during the Paleozoic Era)

Chart showing the Ocoee River during the Paleozoic Era 570 to 240 million years ago
570 to 460 million years ago

Chart showing the Ocoee River 460 to 240 million years ago
460 to 240 million years ago 220 to 185 million years ago (during the Mesozoic Era)

Chart showing the Ocoee River during the Mesozoic Era 220 to 185 million years ago
220 to 185 million years ago

100 million years ago to the present (Cenozoic Era) 100,000 years ago (during the Quaternary Period) 150 years ago 85 years ago Today

Maps

Map of the area surrounding the Ocoee River Gorge
Area surrounding the Ocoee River Gorge.

Topographic map of the Ocoee River Gorge area
Topographic map of the Ocoee River Gorge area.

This map shows part of the Cleveland, Tennessee-North Carolina, 1:100,000-scale topographic map. This map is one example of the many different kinds of maps that the USGS and TVA provide for the public.

Folds and Faults

map icon The Great Smoky fault intersects the Earth's surface near Ocoee Dam No. 1 (Parksville Dam). Faults and folds formed when older rocks were shoved over younger rocks during a continental collision more than 240 million years ago. The fault marks the boundary between two physiographic provinces: the Valley and Ridge province to the west and the Blue Ridge province to the east. Landforms are different on either side of the fault because rocks on the east side are more resistant to weathering and erosion than the younger rocks to the west. The fault is no longer active.

Photograph of folded rock layers near Maddens Branch
Folded rock layers near Maddens Branch. [Photograph by David Usher, U.S. Geological Survey]
Photograph of nearly vertical layers of rock at Boyd Gap
Nearly vertical layers of rock at Boyd Gap. These rocks were deposited as horizontal layers on an ancient ocean floor and tilted upright by plate tectonic forces. [Photograph by David Usher, U.S. Geological Survey]

The Ocoee River

map icon The great power of this river has been harnessed at three points to generate electricity. At Ocoee Dam No. 3, water from the Ocoee No. 3 Lake is diverted to Powerhouse (PH) No. 3 through a tunnel cut through the rock on the west side of the river. The river channel between the dam and the powerhouse normally carries only local flow and, when necessary, flood releases from the lake. A 1,500 ft (457 m) long stretch in this segment of the river was modified to create the Ocoee Whitewater Center, the site of the 1996 Olympic Canoe/Kayak Slalom competition. TVA can release water at Ocoee Dam No. 3 to provide flow for the whitewater course. Unlike a natural stream, most of the flow in this segment of the river can be turned on and off. Downstream, the water is used again as it is diverted through a flume from Ocoee No. 2 Dam to PH No. 2.

The rate of water released for competitions at the Ocoee Whitewater Center is about 1,400 cubic feet per second (628,320 gallons per minute, or 39.6 cubic meters per second). As you consider the amount of turbulence and whitewater that this discharge provides, you might imagine the awesome power of this river when in flood - on November 19, 1906, an estimated discharge of 62,000 cubic feet per second (27,800,000 gallons per minute, or 1,756 cubic meters per second) passed the gaging station site just downstream from PH No. 2.

Photograph of USGS stream gaging station 700 feet downstream from Ocoee Powerhouse No. 2.
USGS stream gaging station 700 feet (213 meters)
downstream from Ocoee Powerhouse No. 2. [Photograph by David Usher, U.S. Geological Survey]

The USGS operates stream-gaging stations along the Ocoee River in cooperation with the Tennessee Valley Authority (TVA) and the Tennessee Ocoee Development Agency. Stream flow data have been collected continuously since 1913 at the gaging station site shown in the photo and on the map (station 03563000 near the former village of Emf, TN). Another recently installed submerged sensor at Slam Dunk (one of the named natural bedrock ledges that forms an eddy in the channel at the Ocoee Whitewater Center) transmits data continuously to TVA. Data from these stations enable TVA to determine discharge rates and maintain flow within a specified range along the canoe/kayak competition course.

Mining at Ducktown

Photorgaph of caved, flooded mine workings at the Burra Burra historic mine site at Ducktown in Copper Basin
View of caved, flooded mine workings at the Burra Burra historic mine site at Ducktown in Copper Basin. [Photograph by David Usher, U.S. Geological Survey]
  Copper was used by Native Americans in the Copper Basin area. European settlers "rediscovered" copper at Copper Basin in the tri-state area of Tennessee, Georgia, and North Carolina in 1843 and started mining it. Mines produced copper, iron, sulfur, zinc, and small amounts of gold and silver. Before 1900, Copper Basin was the largest metal mining district in the Southeast. The last mine closed in 1987.

map icon The early mining and smelting operation at Ducktown devastated the surrounding environment. Trees were cut down and used for fuel to roast the sulfur-rich ore. High concentrations of sulfur dioxide released from the open-air ore roasters harmed vegetation over a large area. Without the tree cover to hold soil in place, the high rainfall in the area removed soil and tons of sediment eroded into the streams. Cooperative reclamation efforts (by the TVA, the Natural Resources Conservation Service, copper companies, and other Federal and State agencies) started in the 1930s and continue today. Thousands of acres of land have been treated and revegetated, and the landscape is being slowly transformed back to forests from the barren "moonscape" that visitors can see preserved at the historic Burra Burra mine site.

Weathering of Pyrite

Photograph showing pyrite in rock outcrops along the Ocoee River
Pyrite in rock outcrops along the Ocoee River. [Photograph by David Usher, U.S. Geological Survey]
  Pyrite (fool's gold) was one of the minerals mined in Copper Basin. Pyrite is iron sulfide and has the chemical formula FeS2. You can see gold-colored cubes of pyrite scattered through many of the rocks along the Ocoee River. Weathering of pyrite has made the rusty-colored stains on some of the outcrops.

When pyrite is exposed to air and water, it can become chemically unstable and change to other minerals, releasing acid in the process. Acidic conditions can develop in streams and be harmful to fish and plants. This acid-generating process can happen naturally, or when roadcuts are made to build highways, or when pyrite-rich rocks are piled up as waste rock tailings from metal or coal mining. Limestone was one of the types of rocks used to modify the river channel at the Ocoee Whitewater Center because limestone counteracts the acid contained in storm runoff.

More Information

This publication is one of a series of general interest publications prepared by the U.S. Geological Survey to provide information about the earth sciences, natural resources, and the environment. To obtain a catalog of additional titles in the series "General Interest Publications of the U.S. Geological Survey," write:

For more information, visit:
U.S. Geological Survey
Forest Service
Tennessee Valley Authority


VIEW a list of other USGS General Interest Publications

URL https://pubs.usgs.gov/gip/ocoee2/
Contact for content: Jane Hammarstrom
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Last modification date: 05-21-07 (akr)