Geology of Pennsylvania

One of the smallest physiographic provinces in the state is confined to Philadelphia, Delaware, and Bucks counties along the Delaware River. Local relief is less than and much of the bedrock is buried under recent alluvial deposits. On the geologic map, "Trenton Gravel" is used to describe most of these sediments. Much of the alluvial sediments that exist here are sand, silt, and clays. The traditional boundary of the coastal plain is the Fall Line. The coastal plain in Pennsylvania was once home to thousands of acres of fresh water tidal marsh. This was important in the early development of Philadelphia and Chester. Many of the small tributaries to the Delaware have cut small but impressive gorges into the bedrock, including the Ridley Creek, the Chester Creek, and the Wissahickon Creek. Flash floods are becoming a local problem in the province. ==Piedmont==

The Piedmont in Pennsylvania is divided into three distinct sections: the Piedmont Uplands, the Piedmont Lowlands, and the Gettysburg-Newark Lowlands. Much of the Piedmont is becoming urbanized and developed. Some of the best farmland in the state is in this region, specifically Lancaster and Chester counties. Piedmont Uplands for the sediments of Pennsylvania This section is characterized by the metamorphic rocks that provide much of the bedrock for this area. The oldest exposed rocks in Pennsylvania are found here and consist of the Baltimore Gneiss. These rocks have a complex history and a vast array of different minerals. They are similar in many respects to their cousins in northern and central Maryland, immediately to the south. Much of the rock was altered during the formation of Rodinia during the Grenville orogeny. These rocks eventually provided the platform for the deposition of sediment that would become the Wissahickon Formation during a rifting of Rodinia. Sea floor spreading continued until a passive margin developed along the new Iapetus Ocean and a beach strandline developed. These sediments eventually became the Chickies Formation. Much of the rocks from this area have been eroded away, but the more erosion resistant diabase has left hills and small elevated regions throughout the section. The erosion patterns of these rocks played a pivotal role in the Battle of Gettysburg. Buckingham Valley A small slice of Paleozoic rocks, mostly carbonates, exists in Buckingham Township. These rocks lie north of the Furlong fault which is an offshoot of the larger Chalfont fault. Buckingham Mountain rises south of the valley and comprises quartzite. The other ridge is less prominent and is underlain by the conglomerates of the Stockton Formation. Karst is a localized problem in this area. ==New England==

A small and fragmented province in northeastern Pennsylvania called the Reading Prong is akin to the crystalline bedrock found in much of New England. This is the southern end of the Hudson Highlands of New York and New Jersey (known as the Ramapo Mountains in New Jersey) and the Taconic Mountains of New York. The granitic rocks and quartzite of this area are highly metamorphosed and are Pre-Cambrian to Cambrian in age. Hills and ridges are locally steep and rounded at the top and form the hills around Reading, and to the south of the Lehigh Valley on South Mountain. ==Ridge and valley==

This region in Pennsylvania, made famous by NASA's LANDSAT images, is the second-largest in the state and home to the famous anthracite fields. The rocks here are severely folded and contain numerous anticlines and synclines that plunge and fold back over each other. There are numerous thrust faults that help create a chaotic mess. Most of the deformation is result of continent to continent collision during the Alleghenian orogeny. There are seven distinct regions of the province and they are listed below. Much of the drainage patterns in the province is trellis. South Mountain South Mountain is the northern tip of the Blue Ridge Mountains. This region is characterized by broad flat ridges with deep narrow valleys. The rocks here are highly metamorphosed igneous and sedimentary rocks with some occasional dolomite. These rocks are Pre-Cambrian in age. Karst features are problematic in the Great Valley. Blue Mountain of Blue Mountain from its east peak The Blue Mountain or Blue Ridge region, like the ridgelines to its north and west, is one of a series of near parallel ridges that run for tens of miles, and are equally likely to be called Ridge or Mountain. Hence Blue Mountain is not to be confused with the Blue Ridge Mountains but instead, represents the sharp escarpment, a step in elevation separating the Appalachian Mountains from the pastoral basin famous as the landscape associated with the Pennsylvania Dutch in southern Pennsylvania called the Great Valley A physiographic province, as are these section titles. Many of Pennsylvania's water gaps cut through Blue Mountain including Delaware Water Gap, Lehigh Gap, Schuylkill Gap, Susquehanna Gap, and Swatara Gap. Also along the ridge, many "wind gaps" also exist. The rocks of the Blue Mountain section include mostly Silurian aged sandstone, conglomerate, siltstone, shale, and some limestone. Blue mountain is also known by the names Kittatinny Mountain (especially in New Jersey) and Hawk Mountain. One of the most prominent rock types of this section is the Shawangunk Formation, which is named after the Shawangunk Ridge of New York state. The sediments that comprise Blue Mountain were deposited as a result of the highlands that formed after the Taconic orogeny. The first wave of sediments were coarse, gray, and poorly sorted. (The Shawngunk Formation) This combination of depositional features means that the source area was relatively close and deposited in a moist climate. These sediments grade into finer reddish sands and silts, (Bloomsburg Formation) as the source area became more distant and/or less productive. The climate during this time was drier. As the conditions became more favorable for the dense forests to survive for hundred of thousands of years, much of the dead plant material became preserved in oxygen-depleted environments. The accumulation of this material became preserved in the vast coal deposits. The rise and fall of the mountains, along with changes in sea level, occurred numerous times (often in conjunction). These cyclical stratigraphic events sequences are preserved in the rock record and are often called cyclothems. By the Late Permian, much of the continental plate collision had subsided; the mountain building however, still continued. All of the sediments deposited during the previous 30 million years became folded and faulted as the supercontinent Pangea was finally formed. It would take 150 million years for the mountains of this area to achieve the shapes seen today. These mountains are steep-sided and valleys are canoe-shaped, largely due to the area's complex folded structure. Most of the coal being mined from this section is from the Pennsylvanian-aged formations. Along with the Mazon Creek fossil field in Illinois, a tremendous amount of plant fossils has been studied from this area. None of the mountains in this section rise above and the river valley is as low as . Appalachian Mountain Standard long, narrow, and steep-sided ridges with narrow valleys define the state in LANDSAT photos. Many of the valleys have karst features due to carbonate rocks that reside in them. Road-building generally follows the valleys and rarely cuts across the ridges. The Pennsylvania Turnpike used tunnels cut through the ridges rather than scaling the mountain tops. Mount Nittany, Tuscarora Mountain, Jacks Mountain, Wills Mountain, and Sideling Hill are five prominent mountains in this section. The section contains Cambrian- through Pennsylvanian-aged sediments all deposited into the Appalachian Basin. During the Appalachian orogeny, these sediments became folded, faulted, and moved around. Only during the past few million years has the landscape we see today taken shape. The relatively softer or easily weathered rocks became valleys while the harder and erosion-resistant rocks became the mountain ridges. The development of this landscape continues to this day. Uplift of the province has caused rivers to cut water gaps through the mountain ranges, and has continuously presented new softer rocks in the valleys to be eroded away. ==Appalachian Plateau==

This is by far the largest province in the state, and most of the rocks in this region are not folded and faulted and sit relatively flat. However, parts of the Appalachian Plateau appear to be mountainous due to erosion caused by streams and glaciers. In western Pennsylvania, large bituminous coal fields exist in rocks with a similar age as the rocks in the anthracite region. Many of the folds in the province are high amplitude and stretch for miles. In glaciated sections, steep canyons developed and much of the terrain have many glacial features. The drainage pattern in this area is dendritic. Glaciated Pocono Plateau The Pocono Mountains section of Pennsylvania is the same geologically as the Catskill Mountains of New York. The red-green-gray sedimentary rocks of the Catskill Formation are the predominant bedrock type in the Poconos. The elevation of the plateau is between and with only a few steep hills such as Camelback Mountain. Much of the rock sits in gently dipping horizontal beds, unlike the neighboring Appalachian Mountain section. Some of the drainage patterns have shifted and only a few of the streams flow into Lake Erie. ==Central Lowlands==

Along with the Coastal Plain Province, the smallest province in the state, the central lowlands are a part of the Great Lakes area and exist along a glacial escapement adjacent to Lake Erie. ==Geologic features==

The following is a list of Pennsylvania geologic features noted for their beauty and/or uniqueness. Periglacial • Hickory Run State Park • Mount Davis Glacial • Archbald Pothole • Grand Canyon of Pennsylvania • McConnells Mill State Park • Moraine State Park • Presque Isle • Promised Land State Park • Ricketts Glen State Park • Worlds End State Park Structural , southwest of Shamokin in the Coal Region • Bear Valley Strip Mine • Chickies Rock • Delaware Water Gap • Pole Steeple • Governor Stable • Ringing Rocks • The Pinnacle ==Rock formations==

Pennsylvania has been updating its base geologic map last printed in 1980. New research has shifted the names of several formations and promoted or demoted many different sequences on the stratigraphic chart. ==References==