Hickory Run State Park
How the rocks came to be, and how the field came to be are really two different stories. The rocks themselves are ancient, laid down as sediments which slowly turned to stone more than 300 million years ago. The rocks are older than the dinosaurs, a part of what geologists call the “Catskill Formation”. This is the type of bedrock underlying a large portion of northeastern Pennsylvania, including most of Monroe, Pike, Wayne and Susquehanna counties. Rub your fingers gently on one of the boulders, and you may be able to feel the fine grains of sediment which were cemented together eons ago. The red color and sandy texture of these grains give the rock its common name: red sandstone. Scattered about Boulder Field you’ll also find conglomerate sandstone – rock with chunks of white, milky quartz crystals embedded within.
Geologists don’t all agree on exactly how this sediment-turned-to-stone became Boulder Field inHickory Run State Park. Signs at the edge of the field’s parking lot describe an ancient valley where the boulders now sit, a valley straddled on either side by cliffs made up of red and conglomerate sandstones. Others suggest the sandstone cliffs weren’t cliffs at all, but a single, gently sloping mass of bedrock situated to the east of the current field (to your left as you enter from the parking lot). Whichever form the sandstone took on, the consensus is this mass of rock was broken into boulders by the same kind of “freeze / thaw” process responsible for most of our potholes and cracked sidewalks; rain or melt water seeps into small crevices in the rock, then freezes solid. Because water expands as it freezes, it expands the crevice in turn. Repeated freezing and thawing continues to widen small spaces in the rock, eventually splitting cliffs or masses of bedrock into boulders, and boulders into smaller pieces over time. The freeze / thaw process was helped along by the area’s glacial climate. Scientists agree most of the rocks were broken apart about twenty thousand years ago, during North America’s last Ice Age. It was then that a massive glacier stopped just short of Boulder Field – only a quarter-mile to the northeast. Though the glacier didn’t deposit the rocks in their current position, its proximity was an important factor in shaping the weather, and therefore in shaping the Hickory Run State Park landscape.
At the time, the area that is now Hickory Run State Park looked much like present-day Greenland. This meant less plant life, which in turn meant more exposed rock. Temperatures fluctuated, things froze, things thawed, and the rocks rolled. Boulder Field was also shaped by “frostheave” – another process to wreak havoc on our present day roads and sidewalks. Water that has seeped into soil also expands when it freezes, sometimes uplifting that soil an inch or more. Some geologists think frost heave was responsible for the depressions found scattered throughout the field – ancient “potholes” that look like odd stone circles, with larger boulders on the outer rim, and smaller ones in the center. Though the glacier has long since receded, freezing and thawing still shape Boulder Field – though much more slowly today. Look closely and you’ll find evidence of recently fractured rocks, their sharp edges standing out in contrast to the more rounded forms worn smooth over time.
Duration of Investigation:
Two digital recorders
samsung video camera
History/ Background Information:
The field comprises about 720,000 square feet (67,000 m2) (16.5 acres (6.7 ha) or 0.026 square miles (0.067 km2)) in area (1,800 feet (550 m) east-west by 400 feet (120 m) north-south).
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