Blue Ridge Mountains
The Blue Ridge Mountains are a physiographic province of the larger Appalachian Mountains range. The mountain range is located in the eastern United States, and extends 550 miles southwest from southern Pennsylvania through Maryland, West Virginia, Virginia, North Carolina, South Carolina, Tennessee, and Georgia.This province consists of northern and southern physiographic regions, which divide near the Roanoke River gap.To the west of the Blue Ridge, between it and the bulk of the Appalachians, lies the Great Appalachian Valley, bordered on the west by the Ridge and Valley province of the Appalachian range.The Blue Ridge Mountains are noted for having a bluish color when seen from a distance. Trees put the “blue” in Blue Ridge, from the isoprene released into the atmosphere. This contributes to the characteristic haze on the mountains and their distinctive color.Within the Blue Ridge province are two major national parks – the Shenandoah National Park in the northern section, and the Great Smoky Mountains National Park in the southern section. The eight national forests include George Washington and Jefferson, Cherokee, Pisgah, Nantahala and Chattahoochee. The Blue Ridge Parkway, a 469-mile (755 km) long scenic highway, connects the two parks and runs along the ridge crest-lines, as does the Appalachian Trail.
Most of the rocks that form the Blue Ridge Mountains are ancient granitic charnockites, metamorphosed volcanic formations, and sedimentary limestone. Recent studies completed by Richard Tollo, a professor and geologist at George Washington University, provide greater insight into the petrologic and geochronologic history of the Blue Ridge basement suites. Modern studies have found that the basement geology of the Blue Ridge is made of compositionally unique gneisses and granitoids, including orthopyroxene-bearing charnockites. Analysis of zircon minerals in the granite completed by John Aleinikoff at the U.S. Geological Survey has provided more detailed emplacement ages.The northernmost extension of the Blue Ridge Mountains, in northern Maryland.Many of the features found in the Blue Ridge and documented by Tollo and others have confirmed that the rocks exhibit many similar features in other North American Grenville-age terranes. The lack of a calc-alkaline affinity and zircon ages less than 1.2 billion years old suggest that the Blue Ridge is distinct from the Adirondacks, Green Mountains, and possibly the New York-New Jersey Highlands. The petrologic and geochronologic data suggest that the Blue Ridge basement is a composite orogenic crust that was emplaced during several episodes from a crustal magma source. Field relationships further illustrate that rocks emplaced prior to 1.078–1.064 billion years ago preserve deformational features. Those emplaced post-1.064 billion years ago generally have a massive texture and missed the main episode of Mesoproterozoic compression.he Blue Ridge Mountains began forming during the Silurian Period over 400 million years ago. Approximately 320 million years ago, North America and Europe collided, pushing up the Blue Ridge. At the time of their emergence, the Blue Ridge were among the highest mountains in the world and reached heights comparable to the much younger Alps. Today, due to weathering and erosion over hundreds of millions of years, the highest peak in the range, Mount Mitchell in North Carolina, is only 6,684 feet (2,037 m) high – still the highest peak east of the Mississippi River in the US.
The English who settled colonial Virginia in the early 17th century recorded that the native Powhatan name for the Blue Ridge was Quirank. At the foot of the Blue Ridge, various tribes including the Siouan Manahoacs, the Iroquois, and the Shawnee hunted and fished. A German physician-explorer, John Lederer, first reached the crest of the Blue Ridge in 1669 and again the following year; he also recorded the Virginia Siouan name for the Blue Ridge (Ahkonshuck).At the Treaty of Albany negotiated by Lieutenant Governor Alexander Spotswood (1676–1740), of Virginia with the Iroquois between 1718 and 1722, the Iroquois ceded lands they had conquered south of the Potomac River and east of the Blue Ridge to the Virginia Colony. This treaty made the Blue Ridge the new demarcation point between the areas and tribes subject to the Six Nations, and those tributaries to the Colony. When colonists began to disregard this by crossing the Blue Ridge and settling in the Shenandoah Valley in the 1730s, the Iroquois began to object, finally selling their rights to the Valley, on the west side of the Blue Ridge, at the Treaty of Lancaster in 1744.During the 1863 Gettysburg Campaign of the American Civil War, the Army of Northern Virginia, Robert E. Lee commanding, slipped across the Potomac to begin the second invasion of the North. They moved slowly across the Blue Ridge, using the mountains to screen their movements until being decisively defeated and turned back in Pennsylvania at the Battle of Gettysburg. This was the key battle of the war, irrevocably turning the tide for the Union and removing any hope of foreign support for the Confederacy.