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The geologic map of Georgia (a state within the United States) is a special-purpose map made to show geological features. Rock units or geologic strata are shown by colors or symbols to indicate where they are exposed at the surface. Structural features such as faults and shear zones are also shown. Since the first national geological map, in 1809, there have been numerous maps which included the geology of Georgia. The first Georgia specific geologic map was created in 1825. The most recent state-produced geologic map of Georgia, by the Georgia Department of Natural Resources is 1:500,000 scale, and was created in 1976 by the department's Georgia Geological Survey. It was generated from a base map produced by the United States Geological Survey. The state geologist and Director of the Geological Survey of Georgia was Sam M. Pickering, Jr. Since 1976, several geological maps of Georgia, featuring the state's five distinct geologic regions, have been produced by the federal government.
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Previous statewide geologic maps of Georgia
The first statewide geologic map of Georgia was published in 1825. It was a 1:1,000,000 scale map of Georgia and Alabama published by Henry Schenck Tanner. In 1849 W.T. Williams published the geological features for the state on a 1:120,000 scale map within George White’s (1849) Statistics of the State of Georgia report. Then in 1871, Dr. Matthew Fleming Stephenson published a 1:1,200,000 scale map of the Geology and mineralogy of Georgia through the Globe Publishing Company of Atlanta. This map was part of a report with the same name. Another statewide map of the geology of Georgia was published in 1876 by G. Little in the Handbook of the State of Georgia by T.P. Janes. In 1885 Georgia Commissioner of Agriculture J.T. Henderson produced a 1:2,500,000 scale map of the geology of Georgia. In 1895 R. T. Nesbitt produced a small-scale geological map of Georgia that was included in a statistical review of the state. The review was described as a Chamber of commerce styled work, that presented the economic mineral resources and geology of the state in a promotional and exaggerated manner. This was the last statewide geological map published in the 19th Century.
Within the 20th Century there were three statewide geological maps produced prior to the 1976 map. The first was a 1 inch to 15 mile map produced by S.W. McCallie in 1908. In 1939, George Willis Stose et al. produced a 1:500,000 scale map that was published by the Georgia Geologic Survey and the United States Geological Survey. This map was reprinted in 1960 by the U.S. Geological Survey. The third map was published in 1968 by the Geological Survey of Georgia. This map was produced by J.W. Smith and M.S. Green, a 1:2,500,000 scale map.
Geologic maps that contained the geology of Georgia
From the beginning of the United States, Georgia geology has been included in maps produced for the entire country. The first geological map of the U.S. was produced in 1809 by William Maclure. In 1807, Maclure undertook the self-imposed task of making a geological survey of the United States. He traversed and mapped nearly every state in the Union. During the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times. The results of his unaided endeavor were submitted to the American Philosophical Society in a memoir entitled Observations on the Geology of the United States explanatory of a Geological Map, together with the nation's first geological map, which were published in the Society's journal Transactions, This precedes William Smith's geological map of England by six years, although Smith's map was constructed using a different classification of rocks. Several reports used Maclure’s geological map to accompany their description of the geology of the U.S. (Beaujour, 1814 and Marcou, 1858). In 1816, within an elementary treatise of mineralogy and geology, Parker Cleaveland produced a geological map of the U.S. In 1843, Charles Moxon produced a small-scale geologic map of the U.S., where Ami Boué produced a geological structure map of the globe. In 1853, Marcou produced a geological map of the U.S. and the British provinces of North America.
In 1856, Henry Darwin Rogers created a similar map of the geology of the U.S. and British North America. There was a short description of the geologic map of the U.S. by Charles Henry Hitchcock in 1872, which had small-scale geological maps included. Hitchcock and William P. Blake published a general geologic map of the U.S. in R.W. Raymond’s Statistics of mines and mining. In 1874, they published a geological map of the U.S. and territories in the U.S. Census 9th Statistical Atlas. Hitchcock and Blake published a summary of this map in the Geological Magazine in 1873. Gray’s geological map of the U.S. was published in the National Atlas special edition at a scale of about 1 inch to 300 miles in 1876 and reprinted in 1886 by the American Institute of Mining Engineers. A geological map of the U.S. east of the Rocky Mountains was produced at the scale of 1 inch to 105.5 miles by Frank H. Bradley. In the 1880s several geological maps of the U.S. were produced. William John McGee offered a detailed description for the U.S. Geological Survey in 1884. In 1887, Hitchcock produced a geological map of the U.S. and parts of Canada that was at the scale of 1 inch to 200 miles, with a review of the various maps of the U.S. that accompanied the geological map of the U.S. In 1895, McGee and J.B. Tolbert produced a 1:15,000,000 scale map of the geology of the U.S.
There have been a host of geological maps of the U.S. produced in the 20th century. Bailey Willis produced a geological map of the U.S. in 1906. George W. Stose produced a 1:2,500,000 scale map in 1932, and a 1:500,000 scale map together with R.W. Smith in 1939. A.K. Lobeck produced a Geologic map of the United States (with text on the reverse side) in 1941 Those are just a few that have been produced. The most recent map being produced is the National Map that is a cooperative project.
The 1976 map
The current geologic map of Georgia was produced in 1976. It was put together mainly in two parts from two teams representing the northern and southern portion of the state.
The map of Georgia is actually a compilation of numerous geological studies and mapping projects that occurred throughout the state and over an extended time period. The major studies that are cited for contribution to the state geologic map fall under three main categories: New mapping by the Georgia Geological Survey, new mapping by the Georgia Geological Survey combined with revised published maps, and published maps with compilation revision only. The majority of the rock units shown on the 1976 map were mapped in 1973 by reconnaissance methods. For some areas, previous authors provided more detailed work than the reconnaissance conducted by the geological survey staff. In those areas, the original author’s work was used in compiling the state map.
Recent geologic mapping in the state of Georgia
More recently, geologic mapping has been undertaken by the Georgia Geological Survey through the STATEMAP project. This project was funded from the National Geologic Mapping Act of 1992. This federal act was for the purpose of producing geologic maps that for 2 decades had been drastically curtailed. It was recognized that “geologic maps are the primary data base for virtually all applied and basic earth-science applications”. This act provided 50% of the funds needed, whereas each state that wanted to participate supplied the other 50% of the funding to complete these various mapping projects. Ultimately this project was to be a part of the National Map and the subsequent databases generated by the various state and national mapping projects.
The geology of Georgia
The geology of Georgia consists of five distinct geologic regions, beginning in the northwest corner of the state and moving through the state to the southeast: the Ridge and Valley region also known as the Appalachian Plateau, the Blue Ridge, the Piedmont, the Fall Line and the Coastal Plain.
Appalachian plateau
The Appalachian Plateau geologic region only passes through the extreme northwest corner of Georgia. During the middle Ordovician Period (about 440 - 480 million years ago), the tectonic plate carrying this area collided with another plate, leading to the creation of a new subduction zone and the beginning of the Appalachians As a result of this and later orogenies, alternating beds of hard and soft Paleozoic sedimentary rocks were folded, looking much like the wrinkles one would find in a kicked floor rug. In Georgia, the Ridge and Valley includes limestone, sandstone, shale and other sedimentary rocks, which have yielded construction-grade limestone, barite, ochre and small amounts of coal. The extent of the Ridge and Valley is bound by the Carters Dam Fault in the east and the Emerson Fault in the south.
Blue ridge
The Blue Ridge geologic region forms the North Georgia mountains. In this region, the highest points in Georgia are found, including Brasstown Bald. The Blue Ridge consists of metamorphic rocks, either metamorphosed equivalents of sedimentary rocks or igneous rocks, and the region includes the metavolcanic rocks of the Georgia Gold Belt. The region also includes igneous intrusions of granite and diabase. From the discovery of gold in the Georgia Gold Belt in 1828, enough gold was mined in the area to cause a branch mint of the United States Mint to be located in Dahlonega, Georgia. Marble and talc are other resources produced in the Blue Ridge in Georgia.
Piedmont
The Piedmont geologic region is composed of igneous and metamorphic rocks resulting from ancient (300 to 600 million year old) sediments that were subjected to high temperatures and pressures and re-exposed about 250 to 300 million years ago. Rocks typical of the region include schist, amphibolite, gneiss, migmatite, and granite. This region is more hilly than mountainous and is marked by lower elevations than the Blue Ridge.
Nevertheless, the Piedmont is home to prominent features like Stone Mountain and the Brevard Fault line which runs parallel to the Chattahoochee River and bisects cities like Suwanee, Atlanta, and Buford.
Fall line
The fall line is the geomorphologic break between the upland region of relatively hard crystalline basement rock and the coastal plain of softer sedimentary rock. The fall line is most prominent when crossed by a river. It is at this point that cities developed, because riverboats could not typically travel any farther inland without portaging. In some locations, the rapid change in elevation of the water, and the resulting energy release, made the fall line a good location for water mills, grist mills, and sawmills. Because of the need for a river port leading to the ocean, and a ready supply of water power, settlements developed where rivers crossed the fall line. In Georgia, the Fall Line extends from Augusta, through Macon, and on to Columbus.
Coastal plain
The Coastal Plain in Georgia is part of a geologic region that extends from New Jersey to Texas and consists of sedimentary rocks deposited in the Late Cretaceous to Holocene periods. It is divided from the Piedmont by the Fall Line, which passes through Georgia from Augusta in the east, then southwestward to Macon, then to Columbus and finally westward to Montgomery, Alabama. The rocks in this region are from the Late Cretaceous to Holocene periods, with some marine and terrestrial fossils and rare fragments of dinosaurs. The main mineral resource of the Coastal Plain in Georgia is kaolin.