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Rocks Rock!

Pennsylvania’s geology story kicks off around 500 million years ago. During that time, the Earth was a much different place to hang out on. While the oceans would still have their blue hue and you’d still be able to breathe, very little else was happening. The land was probably a wash of volcanic colors interspersed with bits of fungus and complex life wasn’t really around, leaving erosion unchecked. So, nearly every time it rained, which happened a lot, huge swaths of sediment were washed down rivers and across the wide, flat river deltas. Pennsylvania happened to be a part of those complex deltas and received a fair share of tiny silica particles.

Those tiny particles slowly accumulated, and the weight of the overhead layers pressed them into some of the strongest rock in the world. These are the rocks that form our mountains today and are widely classified as siliciclastic, meaning made mostly out of silica. This classification puts it into the same groups as quartz, and indeed many of our rocks contain small quartz inclusions. While the hardness of these rocks is legendary, it may as well be sand against the force of moving continents.


Earth - 500 Million Years Ago


A series of massive collisions between the areas that would become North America, Europe and north Africa pressed these layers into a jumble. Fascinating geologic features slowly began to rise from the previously smooth surface. Unlike in other mountainous areas however, the mountains were not pushed up from below. Instead the rocks folded like wrinkles forming on a blanket. These wrinkles ended up becoming the Proto-Appalachian Mountains, whose peaks rivaled that of the modern-day Himalayas.


Earth - 300 Million Years Ago


Eventually the other continental plates shifted and began to move apart creating the Atlantic Ocean in the process. The mountains left behind began the long and slow journey of erosion, now with plants! Eventually the hard outer layers of the mountains cracked, exposing the softer layers of limestone inside. Rapidly, the cores of these gargantuan hills washed away to form much of the east coast. What we are left with are the roots of the old mountains.

What does this all mean? It means that the rocks that make up our modern mountains are much older than those in the valleys they fringe. So, the next time you climb Mt. Nittany, think about how you are walking on rocks that were at the bottom of the ocean a half-billion years ago!


The massive parallel mountains are relics of that older chain and they presented many challenges to early native people, and eventually to European settlers during their colonization efforts. While settlements quickly spread across areas with large placid rivers or costal seaways, the heart of Pennsylvania remained mostly untouched wilderness. While much of the continent was fermenting rebellion against their European masters, central Pennsylvania was devoid of major settlements. It took well into the late 1700’s before swaths of people flocked into the wide fertile valleys.

Today those inclined to walk the inclines can experience just what made these little mounds insurmountable to those without the benefit of internal combustion engines. Each of our ridges usually has two faces, the face that makes the original mountain plane and the eroded layers. The original faces are often uniform and rise consistently from the valley floors. The eroded faces are anything but smooth, often containing incredibly steep sections and are broken by a series of smaller ridges and valleys. As fortune would have it, many of the faces pointing towards our major population centers in Centre County are the eroded variety. However, a couple hundred million years has blunted the teeth of these climbs and there are ample opportunities to cheat through the many gaps formed by wind or water.

If you want to see interesting geology in central Pennsylvania all you have to do is look down. There are fascinating formations across our entire region, but here are some of the best places to look at the more prominent features.

Adventuring along the Lower Trail gives a glimpse into the incredible power water has to shape our landscape. The adjacent Juniata has spent tens-of-millions of years carving its way through that tough silica-based rock, leaving behind a meandering path. Nearby, roadway cuts into the mountain give a clear sight into the intricate folds and faults that make up the layers of stone. The 17-mile trail runs between an area near Canoe Creek State Park in Blair County to near Alexandria in Huntingdon County.

Mt. Nittany in Lemont, PA is a prominent landmark that just so happens to be a perfect example of the inverted geography. When making the trek to the top people often become puzzled as to why there is so much sand at the top. The top of Mt. Nittany is the original bottom of the rivers that eroded the first peaks of the Appalachians. The parking area to Mt. Nittany can become congested on weekends, especially when the weather is beautiful, so consider hiking early or during business hours to avoid crowded trails.

A trip to Poe Paddy State Park near Millheim, PA gives guests the opportunity to not only hike on the ancient rocks, but also to go through them via the Poe Paddy Tunnel. After passing through a couple hundred million years the Mid State Trail continues past a series of large boulder fields that are the collapsed slopes of mountains. Here guests can see the effect the fast eroding materials have on the stronger ones that lay above them.

The Scotia Barrens, a.k.a. State Game Lands 176 in Warriors Mark, PA, is a unique point not because of any majestic mountain but because of a subterranean feature. The underlying limestone is so porous, and the soil is so well drained that surface water features are almost nonexistent. The water that falls in this area makes an incredible underground journey before emerging well-filtered and chilled at one of a number of springs feeding into Spring Creek.

The Spring Creek Canyon, as the name implies, is a gorgeous feature carved out by the waters of Spring Creek. At the southwest trailhead on Rock Road in Benner Township, the many layers of limestone and shale that form the valley floors are exposed and readily observed. Trails along the Spring Creek Canyon can also be accessed via the Fisherman’s Paradise parking lot off Spring Creek Rd. in Bellefonte, and from the Shiloh Rd. exit off 322 in State College.


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