So in a nearby earth cache I lightly touched on a era in which the earth was going through many difficult growing pains. One the "growth spurts" we will be addressing in this earth cache is the Ozark Plateau upheaval, along with weathering effects and the affects they have on our limestone.
Ozark Plateau
So you are standing here in front of GZ no doubt reading the information that the parks and trails department was nice to offer you, but perhaps you are wondering what or more so where is the Ozark Plateau? Very good question, the Ozark Plateau is a region known as the Ozak Plateau Region and is a thoroughly dissected area with steep valley walls and narrow floors. This region is divided into three broad plateau surfaces based on elevation and age of surface rocks.
Salem Plateau
The Salem Plateau contains the oldest rock at the surface - Ordovician dolostones, sandstones and limestones. This is also the lowest plateau surface with some of the highest elevations reaching between 800 and 1400 feet above sea level.
The Salem Plateau, north and east of the Springfield Plateau, is separated from it by an abrupt drop. The abrupt change in elevation is apparent at Eureka Springs (Carroll County), where its location on the boundary of the two plateaus gives it its mountainous character. Like the Springfield Plateau, the Salem Plateau often forms extensive plains, as at Berryville (Carroll County). Several distinct areas of hills have been cut into the plateau by rivers, most prominently along the White River and its tributaries. Other extensive hills have been cut by the Spring and Strawberry rivers. The Salem Plateau is often underlain by dolomite or dolostone, similar to limestone. Although dolostone is not dissolved by water as readily as limestone, caves are present, as well as large springs such as the one at Mammoth Spring (Fulton County).
The plateau surface and level hilltops have rocky soil originally covered with oak forests, open oak woodlands, and open rocky glades. Large areas were described in the nineteenth century as “barrens,” implying exposed rock and thin soil, with limited herbaceous and woody plant cover. Near Berryville were several prairies that surrounded low hills with forested sides and prairie on the tops, known as “bald knobs.”
The Salem Plateau had few areas easily adapted to agriculture, such as areas of deep alluvial soil or prairie. However, beginning in the late nineteenth century and extending through the twentieth century, recreational development became increasingly important. In the late nineteenth century, Eureka Springs developed along the Missouri and North Arkansas Railroad as a tourist destination known for “healing springs.” Although the railroad eventually failed, Eureka Springs has remained a tourist destination into the twenty-first century.
Springfield Plateau
The Springfield Plateau contains mostly Mississippian age limestone and chert from the Boone Formation at the surface. The plateau surface consists mostly of gently rolling hills or an undulating topography, however in some places the Boone Formation forms steep hillsides separated by ravine-like drainages.
The Springfield Plateau, adjacent to and north of the Boston Plateau, is usually abruptly lower. In many areas, the plateau surface, at an elevation of about 1,800 feet, forms extensive plains. Hilly areas occur where rivers and their tributaries cut into the plateau surface, most notably in the vicinity of the White River. Also, as streams like the Buffalo National River cut through the plateau down to the level of the White River, they sometimes carve spectacular bluffs.
The Springfield Plateau is underlain by limestone and chert, a flint-like rock. Since limestone is easily dissolved by water, cave and solution (karst) features are prominent. Surface water may drain directly into channels in limestone, where it can move rapidly and without filtration to the surface as a spring, at a location that is unpredictable without extensive testing. Therefore, water pollution problems are of particular concern in this region. In addition, both caves and the small streams fed by springs known as spring runs support aquatic species vulnerable to extinction.
South-facing, cherty slopes are occupied by shortleaf pine and hardwood forests, while hills and mountains underlain by limestone are often occupied by hardwood forests. Rocky, open glades with exposed limestone or chert are extensive and common. Prairies on level plateau surfaces with thin soils were extensive, but almost all have been converted to pasture, cities, and other developed areas. The most extensive prairies extended from Fayetteville to Rogers (Benton County), and also near Harrison (Boone County). These areas have experienced considerable urban growth.
Boston Mountain Pleateau
The Boston Mts. Plateau contains the youngest rock at the surface - Early Pennsylvanian sandstones and shales with minor limestones. This is also the highest plateau surface with some of the highest elevations reaching 2200-2500 feet above sea level.
At up to 2,600 feet, the Boston Plateau, usually referred to as the Boston Mountains because of its ruggedness, is the highest of the Ozark Mountains. It extends as a belt across the southernmost Ozarks, generally parallel to and to the north of Interstate 40. Typical rock types are sandstone and shale. Although the elevation of the mountains is similar, the highest are in and near Newton County. The elevation there causes higher precipitation and lower temperatures than elsewhere in the Ozarks. Streams are generally small, and the headwaters of many of the well-known rivers of the Ozarks occur in the Boston Mountains, including the White, Buffalo, King’s, Mulberry, Big Piney, and Little Red rivers.
In most areas of the Boston Mountains, oak and hickory forests predominate, while warm, south-facing slopes on sandstone have extensive areas dominated by shortleaf pines. The cool, moist conditions of protected ravines, particularly in the highest mountains, support forests with beech or sugar maple that are of limited extent elsewhere in the Ozarks.
Uplifting Mother Earth
To better understand our little coner of the earth we are going to need to jump into a time maching about 500 million years ago. The Ozark Plateau was once a shallow continental shelf underwater. The shelf that became the Ozark Plateau was alternately above or under water for millions of years. First, shells of sea organisms accumulated to form sediment layers of that became limestone and dolostone units. Later, when the area to the north was above sea level, streams flowed down the land and into the ocean, depositing layers of sediment on the shelf. These layers were made of sand, silt and clay and eventually hardened into sandstone, siltstone and shale. During this time continental plates were moving very slowly. Later (about 320 million years ago), when two plates collided to form the Ouachita Mountains, portions of the sea floor that were farther from the collision were also gently lifted above the water to form a flat plateau. This uplifted plateau is the Ozark Plateau. A plateau is a raised land formation with a flat top. Wind, rain and rivers have eroded the Ozark Plateau over millions of years, creating steep valleys. This erosional continues today. Its pretty cool to see 500 centuries at work in just one paragraph, and to touch it here at GZ.
Did you know?
Ozarks are a physiographic, geologic and cultural highland region of the central United States covering much of the south half of Missouri, an extensive portion of northwest and north central Arkansas and extending westward into northeast Oklahoma and extreme southeast Kansas. Although they are refered to as mountains, the region is actually a high and deeply dissected plateau?
So now that we learned a little bit about the Ozark Plateau Region, take a moment to study ground zero, as well as the placards for GZ. With the information above, and information at GZ you should be able to answer the following questions. You have 24 hours to send me an email (found in my geocaching profile) with the correct answers. Failure to do so will result in the removal of your "Found it log". Please add the GC code and title in the subject line. If you are sending answers for multiple people in your group, please add all the names in your email to ensure they don't have their log deleted :) Photos with you or in the group of the area would be greatly appreciated.
Requirements: (Do not post the answers in the log)
1 Is Ground Zero located in the Mountains or Plateau?
2 According to GZ information, what was the weathering used to create this unique formation?
3 Is the limestone split in half, thrids or quarters?
4 What plateau sub-region is Ground Zero located in?
5 What is the title of the placard at Ground Zero for this Earth Cache?
6 What visual clues prove that GZ was underwater milions of years ago?
7 What is the name of the trail you are on?
8 In your own words breifly explain what happened to the limestone here at Ground Zero.
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