exposed on Tussey Mountain, where the
Raystown Branch of the
Juniata River and
U.S. Route 30 pass through west of
Everett Tussey Mountain is in the
Ridge and Valley province of the
Appalachian Mountains.
Brush Mountain,
Mount Nittany and
Bald Eagle Mountain ridges, are part of the same
Paleozoic anticline rock formation consisting of older
Ordovician Bald Eagle Formation Sandstone and
Juniata Formation Shale, and younger
Silurian Tuscarora Formation Quartzite. During the
Appalachian orogeny, these layers
folded up with the underlying and overlying layers into the Nittany Arch. The arch was a
Himalayan scale mountain that towered above what is now
Nittany Valley, where the oldest rock layers from deep within the
eroded mountain are now exposed. The Tuscarora Quartzite is more resistant to erosion than Bald Eagle Sandstone, and both are more durable than the Juniata Shale sandwiched in-between. Softer rock layers on either side of these eroded, leaving the double crested Tussey Mountain ridge, with a depression between the higher eastern and lower western ridge lines found on the northern section of the ridge. Since the rock layers on these ridges slope down to the east, the Tuscarora Formation underlies the higher crest, where it protected the east slope from erosion. Drainage from the upper slope has cut a series of small ravines in the lower ridge line, leaving a terraced lower slope in the Bald Eagle Formation. On the neighboring Bald Eagle, Brush, and Dunning Mountain ridges to the west that formed the opposite side of the ancient mountain, the same three rock layers are exposed in reverse order, with the oldest rocks in-between, near the hinge of the fold. ==See also==