Washington’s Trail through Post Glacial Butler, PA
In 1753, the future first president of the United States, George Washington, was dispatched to Western Pennsylvania to deliver a message to the French soldiers stationed near Presque Isle. Only twenty-one years old, young Washington traveled north from Fort Duquesne through modern day Butler County. Although aware of the critical and dangerous nature of the mission, it is unlikely that that the young explorer was aware that he was traversing a land of physical features shaped by a 100,000 years of geological history (WTA, 2013).
After embarking from present day Pittsburgh, Pennsylvania, Washington first entered Butler County on November 30, 1753. Traveling north on an Indian trail, the first sign of the area’s cataclysmic past would have appeared out of place from the rolling hills typical of the Western Pennsylvanian landscape. Peering down into a valley over 400 feet deep, the mighty gorge was littered with enormous boulders, thus framing the Slippery Rock Creek. These relict boulders of rock types foreign to the area are known as “glacial erratics” and are indicative of the strength of the encroaching glacier. As defined by the National Snow and Ice Data Center, “Glacial erratics are stones and rocks that were transported by a glacier, and then left behind after the glacier melted. Erratics can be carried for hundreds of kilometers, and can range in size from pebbles to large boulders. Scientists sometimes use erratics to help determine ancient glacier movement.” (NSIDC, 2014)
To understand the unique aspects of a gorge created in just a few days, it is necessary to look back to the events which occurred 100,000 years ago. Described by James Lovelock in his book, The Ages of Gaia: A Biography of Our Living Earth, Milankovitch Cycles define the regular consistency of the Earth's glacial and interglacial periods. “Variations in the Earth's eccentricity, axial tilt, and precession comprise three dominant cycles. Taken in unison, variations in these three cycles creates alterations in the seasonality of solar radiation reaching the Earth's surface. These times of increased or decreased solar radiation directly influence the Earth's climate system, thus impacting the advance and retreat of Earth's glaciers.” (Lovelock, 1995)
About 2 million years ago, thick masses of continental ice started to accumulate in central and northeast Canada. Periodically, the ice would spread southward as great ice sheets that were hundreds to thousands of feet thick. Reaching as far south as Pennsylvania, the first two ice sheet deposits eroded away their effect on the landscape and stream patterns (Fleeger, et al. 2003). During the last Ice Age, ice dammed the rivers and lakes that covered much of the region. Towards the end of glacial times, Muddy Creek was blocked with glacial debris. The resulting lake filled most of the valleys in present day Butler County. As climate warmed, the ice retreated and...