Ozarks
The Ozarks, also known as the Ozark Mountains, Ozark Highlands or Ozark Plateau, are a physiographic region in the U.S. states of Missouri, Arkansas, and Oklahoma, as well as a small area in the southeastern corner of Kansas. The Ozarks cover a significant portion of northern Arkansas and most of the southern half of Missouri, extending from Interstate 40 in central Arkansas to Interstate 70 in central Missouri.
There are two mountain ranges in the Ozarks: the Boston Mountains of Arkansas and Oklahoma, as well as the St. Francois Mountains of Missouri. Wahzhazhe Summit, is the highest point in the Ozarks at, and is located in the Boston Mountains, in the westernmost part of Newton County, Arkansas, east of Boston, Madison County, Arkansas. Geologically, the area is a broad dome with the exposed core in the ancient St. Francois Mountains. The Ozarks cover nearly, making it the most extensive highland region between the Appalachians and Rockies. Together with the Ouachita Mountains, the area is known as the U.S. Interior Highlands.
The Salem Plateau, named after Salem, Missouri, makes up the largest geologic area of the Ozarks. The second largest is the Springfield Plateau, named after Springfield, Missouri, nicknamed the "Queen City of the Ozarks". On the northern Ozark border are the cities of St. Louis and Columbia, Missouri. Significant Ozark cities in Arkansas include Fayetteville, Rogers, Bentonville, Springdale, Eureka Springs, and Fort Smith. Branson, just north of the Arkansas–Missouri border, is a tourist destination where Ozark culture is popularized.
Etymology
The origin of the name is uncertain. The toponym Ozarks may derive from an English-language adaptation of the French abbreviation . In the decades prior to the French and Indian War of 1754 to 1763, referred to France's trading post at Arkansas Post, located in the wooded Arkansas Delta lowland area above the confluence of the Arkansas River with the Mississippi River.Another possible etymological origin might be the French phrase, meaning " of the arches", in reference to the dozens of natural bridges formed by erosion and collapsed caves in the Ozark region. These include Clifty Hollow Natural Bridge in Missouri, and Alum Cove in the Ozark–St. Francis National Forest.
By the early 20th century, the term "Ozarks" had entered common parlance.
Physiographic subregions
The Ozarks consist of five physiographic subregions: the Boston Mountains of north Arkansas and Cookson Hills of east Oklahoma; the Springfield Plateau of southwest Missouri, northeast Oklahoma, and northwest Arkansas and including Springfield, Joplin and Monett/Aurora in Missouri, Tahlequah in Oklahoma, and Fayetteville and Harrison in Arkansas; the White River Hills along the White River, including Branson and Mountain Home to Batesville; the Salem Plateau or Central Plateau, which includes a broad band across south central Missouri and north central Arkansas including the Lebanon, Salem and West Plains areas; the Courtois Hills of southeastern Missouri; the Osage-Gasconade Hills around the Lake of the Ozarks; the Saint Francois Mountains; and the Missouri River and Mississippi River border areas along the eastern and northeastern flanks.Karst features such as springs, losing streams, sinkholes and caves are common in the limestones of the Springfield Plateau and abundant in the dolomite bedrock of the Salem Plateau and Boston Mountains. Missouri is known as "The Cave State" with over 7,300 recorded caves, second in number only to Tennessee. The majority of these caves are found in the Ozark counties. The Ozark Plateaus aquifer system affects groundwater movement in all areas except the igneous core of the St. Francois Mountains. Geographic features include limestone and dolomite glades, which are rocky, desert-like areas on hilltops. Kept open by periodic fires that limit growth of grasses and forbs in shallow soil, glades are home to collared lizards, tarantulas, scorpions, cacti and other species more typical of the Desert Southwest.
The Boston Mountains contain the highest elevations of the Ozarks, with peaks over, and form some of the greatest relief of any formation between the Appalachians and Rocky Mountains. The Ouachita Mountains to the south rise a few hundred feet higher, but are not geographically associated with the Ozarks. The Boston Mountains portion of the Ozarks extends north of the Arkansas River Valley, is approximately long, and is bordered by the Springfield and Salem Plateau to the north of the White River. Summits can reach elevations of just over, with valleys deep. Turner Ward Knob is the highest named peak. Found in western Newton County, Arkansas, its elevation is. Nearby, five unnamed peaks have elevations at or slightly above. Drainage is primarily to the White River, with the exception of the Illinois River, although there also is considerable drainage from the south slopes of the Boston Mountains to the Arkansas River. Major streams of this type include Lee Creek, Frog Bayou, Mulberry River, Spadra Creek, Big Piney Creek, Little Piney Creek, Illinois Bayou, Point Remove Creek, and Cadron Creek. Many Ozark waterways have their headwaters in the uplands of the Boston formation, including the Buffalo, Kings, Mulberry, Little Red and White rivers.
Topography is mostly gently rolling in the Springfield and Salem plateaus, whereas the Saint Francois Mountains are more rugged. Although the Springfield formation's surface is primarily Mississippian limestone and chert, the Salem Plateau is made of older Ordovician dolomites, limestones, and sandstones. Both are rife with karst topography and form long, flat plains. The formations are separated by steep escarpments that dramatically interrupt the rolling hills. Although much of the Springfield Plateau has been denuded of the surface layers of the Boston Mountains, large remnants of these younger layers are present throughout the southern end of the formation, possibly suggesting a peneplain process. The Springfield Plateau drains through wide, mature streams ultimately feeding the White River.
Geology
The St. Francois Mountains in the northeastern Ozarks are the eroded remnants of an ancient range which form the geological core of the highland dome. The igneous and volcanic rocks of the St. Francois Mountains are the exposed remains of a Proterozoic mountain range hundreds of millions of years old. The remaining hills are the exposed portion of an extensive terrane of granitic and rhyolitic rocks dating from 1485 to 1350 mya that stretches from Ohio to western Oklahoma. The core of the range existed as an island in the Paleozoic seas. Reef complexes occur in the sedimentary layers surrounding this ancient island. These flanking reefs were points of concentration for later ore-bearing fluids which formed the rich lead-zinc ores that have been and continue to be mined in the area. The igneous and volcanic rocks extend at depth under the relatively thin veneer of Paleozoic sedimentary rocks and form the basal crust of the entire region.File:Taum Sauk precambrian-cambrian unconformity.jpg|thumb|right|Grey dolomite laid down c. 500 mya nonconformally overlies reddish rhyolite that formed close to 1500 mya in the St. Francois Mountains.
A major unconformity in the region attests that the Ozarks were above sea level for several hundred million years from the time of the volcanism in the Precambrian until the mid-Cambrian with an erosionally produced relief of up to. The seas encroached during the late Cambrian producing the Lamotte Sandstone, thick, followed by carbonate sedimentation. Coral reefs formed around the granite and rhyolite islands in this Cambrian sea. This carbonate formation, the Bonneterre, now mostly dolomite, is exposed around the St. Francis Mountains, but extends in the subsurface throughout the Ozarks and reaches a thickness of. The Bonneterre is overlain by of dolomite, often sandy, silty or cherty, forming the Elvins Group and the Potosi and Eminence formations. Withdrawal of the seas resulted in another unconformity during the latest Cambrian and early Ordovician periods. Hydrothermal mineralizing fluids formed the rich lead ore deposits of the Lead Belt during this time.
Sedimentation resumed in the Ordovician with the deposition of the Gunter sandstone, the Gasconade dolomite and the prominent Roubidoux sandstone and dolomite. The sandstone of the Roubidoux forms prominent bluffs along the streams eroding into the southern part of the Salem Plateau. The Roubidoux and Gunter sandstones serve as significant aquifers when present in the subsurface. The source of the sands is considered to be the emerging Wisconsin Dome to the northeast. The Ozark region remained as a subsiding shallow carbonate shelf environment with a significant thickness of cherty dolomites such as the Jefferson City, Cotter and Powell formations.
Portions of the Ozark Plateau, the Springfield Plateau of southwest Missouri and northern Arkansas, are underlain by Mississippian cherty limestones locally referred to as "Boone chert", consisting of limestone and chert layers. These are eroded and form steep hills, valleys and bluffs.
The Boston Mountains are a high and deeply dissected plateau. The rocks of the region are essentially little disturbed, flat-lying sedimentary layers of Paleozoic age. The highest ridges and peaks are capped by Pennsylvanian sandstone such as the basal Atoka and the "Middle Bloyd". The deeply eroded valleys are cut into Mississippian limestone and below that layer Ordovician dolomite.
During the Pennsylvanian period, the Ozark Plateau was uplifted as a result of the Ouachita orogeny. During the late Paleozoic, the deep ocean basin that existed in central and southern Arkansas was lifted when South America collided with North America, creating the folded Ouachita Mountains and uplifting the Ozark plateau to the north.