REMARKS: A large sinkhole spring (median flow 8000 gallons per minute) and collapsed cave in the Loysburg Formation (Ordovician age). Water wells up in the center of the sink and exits via a natural bridge (arch) which is part of the former cave system; it is the eighth largest spring in Pennsylvania.
REFERENCES: Flippo, H. N., Jr. [1974], Springs of Pennsylvania Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.
Rogers, H. D. [1858], The geology of Pennsylvania, Pennsylvania Geological Survey, 1st ser., v. 1, 586 p.
REMARKS: The mineral occurs in layers of irregular thickness in a hard calcareous shale of the Tonoloway Formation (Silurian age). This is the locality where this mineral was first discovered, described, and named.
REFERENCES: Klaproth, M. H. [1797], Chemische untersuchung des Schwefelsauren strontianits, aus Pensilranien, Beitraege zur Chemischen Kenntiss Der Mineralkoerper Berlin, v. 2, p. 92-98.
Mangus, M. D. [1946], The type locality of celestite, M. S. thesis, The Pennsylvania State University, University Park, Pennsylvania.
Young, C. A. [1875], The occurrence of celestine in Blair County, Pennsylvania, Academy of Natural Sciences of Philadelphia, Proceedings, no. 28, p. 127-128.
REMARKS: Vertical beds of the Silurian Tonoloway Limestone form three finger-like projections skyward.
REMARKS: This is the finest display of Late Paleozoic rocks to be found along the Allegheny Front; the rock section extends for more than 45,000 feet and exposes some 7000 feet of rock thickness. Mostly shales and sandstones are exposed; they range in geologic age from the base of the Upper Devonian Lock Haven Formation to the base of the Pennsylvanian Conemaugh Group.
Engineers had been dreaming for two decades of how to conquer the Alleghenies by rail. In 1847 the Pennsylvania Railroad re-surveyed the route west and decided on the route that exists today. About 5 miles west of Altoona the valley ran abruptly into the Allegheny Front. To go directly across the valley would have meant building a bridge that had a 4.37 percent grade, which was far too steep for practical rail operations. Instead, they sliced off the face of the mountain so the tracks would make a large semicircle; this became the Horseshoe Curve. The Horseshoe Curve is an engineering marvel of 1854. It has won the engineering world's admiration for the ingenuity of its idea, for the skillful design of its details, and for the engineers' courage in undertaking such a large construction task before the day of the bulldozer and the steam shovel. The Horseshoe Curve has become a scenic wonder of the world.
REFERENCES: Swartz, F. M. [1965], Guide to the Horseshoe Curve section between Altoona and Gallitzin, central Pennsylvania Pennsylvania Geological Survey, 4th ser., General Geology Report 50, 58 p.
REMARKS: Blair County's version of Old Faithful; the aquifer is the Nittany Formation (Ordovician age). Discharge as measured in November 1971 was 4280 gallons per minute; the spring is used as a public water supply.
REFERENCES: Flippo, H. N., Jr. [1974], Springs of Pennsylvania, Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.
REMARKS: The zinc-lead occurances in Sinking Valley are located in Ordovician limestones and dolomites. Mineralization is localized along fractures; these fractures are filled with barite, sphalerite, galena, and calcite. Recent weathering altered much of the sphalerite to smithsonite and some of the galena to anglesite.
The American Revolution was already underway when the scarcity of lead for bullets threatened the fate of the colonies. Brigadier General Daniel Roberdeau took a leave of absence from his seat in the Continental Congress to come to the Sinking Valley area to find lead. Active mining began here in 1778. At his own expense, General Roberdeau built the fort that bears his name and had government militia installed to protect the lead miners. Also, settlers of the area found shelter at Fort Roberdeau during times of Indian unrest. As a Blair County bicentennial project. Fort Roberdeau has been reconstructed on the original site.
REFERENCES: Geyer, A. R., Smith, R. C. II, and Barnes, J. H. [1976], Mineral collecting in Pennsylvania, 4th ed., Pennsylvania Geological Survey, 4th ser., General Geology Report 33, p. 50-53.
Zeller, R. A. [1949], The structural geology and mineralization of Sinking Valley, Pennsylvania, M. S. thesis, The Pennsylvania State University, University Park, 71 p.
REMARKS: Excellent view from the Allegheny Front of the Valley and Ridge province to the east, Altoona, and a six-county area; the elevation is 2580 feet above sea level. The bedrock beneath the rim of the Allegheny Front here is the hard, tough Burgoon Sandstone (Mississippian age) which, due to its weather-resistant qualities, causes the great difference in elevation between the limestone valley and this site.
REFERENCES: Glover, A. D., and Faill, R. T. (in preparation), Geology and mineral resources of the Altoona 15-minute quadrangle, Blair, Cambria, Clearfield, and Centre Counties, Pennsylvania Pennsylvania Geological Survey, 4th ser., Atlas 86.