Quehanna Wild Area - Geology and Climate

Geology and Climate

Quehanna Wild Area lies at an elevation of 1,896 feet (578 m) on the Allegheny Plateau. The area falls into portions of two distinct geological physiographic provinces, with all but the northernmost part in the Pittsburgh Low Plateau, known for its coal and mineral deposits, and characterized by steep-cut stream beds. The northernmost part of the wild area, including Marion Brooks Natural Area, is in the Deep Valleys section, home to some of the most remote and wild areas of the state; streams here have cut deep valleys with steep-sided slopes. In the southern part of Quehanna Wild Area, the Mosquito Creek gorge is up to 500 feet (150 m) deep, while the Red Run gorge in the north is almost 900 feet (270 m) deep.

The Allegheny Plateau formed in the Alleghenian orogeny some 300 million years ago, when the part of Gondwana that became Africa collided with the landmass that became North America, forming Pangaea. In the dissected plateau, years of erosion have cut away the soft rocks, forming the valleys, and leaving the hardest rocks relatively untouched. The land on which Quehanna Wild Area sits was part of the coastline of a shallow sea that covered a great portion of what is now North America in the Pennsylvanian subperiod. The high mountains to the east of the sea gradually eroded, causing a buildup of sediment made up primarily of clay, sand and gravel. Tremendous pressure on the sediment caused the formation of the rocks that are found today.

At least five major rock formations from the Devonian and Carboniferous periods are present in Quehanna Wild Area. The youngest of these, which forms the highest points on the plateau, is the Pennsylvanian Allegheny Formation, which has clay, coal, limestone, sandstone, and shale. Below this is the Pennsylvanian Pottsville Formation, a gray conglomerate that may contain sandstone, siltstone, and shale, as well as anthracite coal, and which forms much of the Quehanna plateau. The next formations are found in the valleys and gorges which the creeks have eroded over time. The first of these is the Mississippian Pocono Formation, which is buff colored with shale, coal, and conglomerate inclusions; parts of this formation are also known as the Burgoon Sandstone. Below this is the late Devonian and early Mississippian Huntley Mountain Formation, which is made of relatively soft grayish-red shale and olive-gray sandstone. The lowest and oldest layer is the red shale and siltstone of the Catskill Formation.

The Allegheny Plateau has a continental climate, with occasional severe low temperatures in winter and average daily temperature ranges (the difference between the daily high and low) of 20 °F (11 °C) in winter and 26 °F (14 °C) in summer. Quehanna Wild Area is part of the Mosquito Creek and Wykoff Run watersheds, where the mean annual precipitation is 40 to 42 inches (1,016 to 1,067 mm). Weather records are not available for Quehanna Wild Area, but they are known for the nearby village of Karthaus. The highest recorded temperature at Karthaus was 101 °F (38 °C) in 1988, and the record low was −22 °F (−30 °C) in 1994. On average, February is the coldest month, July is the hottest month, and June is the wettest month.