Geology of Pennsylvania

Each province has its own economic advantages and geologic hazards and plays an important role in shaping everyday life in the state.

Pennsylvania also has reserves of natural gas from both deeply buried source rocks and coal-bed areas.

The coastal plain in Pennsylvania was once home to thousands of acres of fresh water tidal marsh.

The sediments that were deposited in a sea between an island-arc and the Iapetus eventually were squeezed and deformed along a subduction zone.

These rocks are relatively younger in age than the surrounding uplands and are likely the result of a quiet stretch of shallow sea deposition.

[9] 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.

A small and fragmented province in northeastern Pennsylvania called the Reading Prong is akin to the crystalline bedrock found in much of New England.

Rocks that characterize this region include: limestone, dolomite, slate, shale, sandstone, siltstone, and some scattered basalt.

Almost all of the rocks in the Great Valley in Pennsylvania are Ordovician in age and were deposited during a quiet period before the Taconic orogeny.

These carbonate rocks are used for variety of purposes including, crushed stone, cement manufacturing, fertilizers, and coal-mine dust (reduces acid mine drainage)[12] Karst features are problematic in the Great Valley.

The rocks of the Blue Mountain section include mostly Silurian aged sandstone, conglomerate, siltstone, shale, and some limestone.

The sediments that comprise Blue Mountain were deposited as a result of the highlands that formed after the Taconic orogeny.

These sediments grade into finer reddish sands and silts, (Bloomsburg Formation) as the source area became more distant and/or less productive.

Since the North American Plate was near the equator, a tropical climate existed and allowed dense forests to flourish.

Beginning in the Late Mississippian, forests of Lycopodiophyta, Arthrophyta, Pteridophyta, and Pteridospermatophyta began to grow in these plains.

[13] 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.

All of the sediments deposited during the previous 30 million years became folded and faulted as the supercontinent Pangea was finally formed.

These mountains are steep-sided and valleys are canoe-shaped, largely due to the area's complex folded structure.

This action has left many talus slopes at the base of Moosic Mountains, and the soils often contain large boulders that make excavation difficult.

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.

Much of the rock sits in gently dipping horizontal beds, unlike the neighboring Appalachian Mountain section.

The Big Bushkill Creek cuts a gorge through this section and has many waterfalls, especially around the area of Resica Falls Scout Reservation.

As the name implies, the streams of this area have cut deep valleys with steep sided-slopes on the surrounding ridges.

The Allegheny Front reaches its highest elevation in Pennsylvania at Blue Knob, 3,136 feet (956 m), an unusual bulge along this symmetrical ridgeline.

This section includes Pennsylvania's highest point, Mount Davis, which stands at 3,213 feet (979 m) above sea level.

Unlike the Appalachian Mountain section, the streams of this area have not cut deep and well defined valleys into the earth.

Much of the drainage pattern is dendritic with a little trellis where erosion resistant rocks have created higher and more well defined ridges.

[3] This region is also home to two national stories: the Quecreek Mine Rescue and the crash of United Airlines Flight 93.

Much of the 64.4 billion tons of bituminous coal that is remaining in the state resides under these hills in near horizontal beds.

[3] This section consists of high, broad, and flat uplands cut by sharp and shallow river valleys.