REMARKS: The fifth largest spring in Pennsylvania, having a median flow of 12,500 gallons per minute. The spring rises from fractures in the limestone and dolomite of the Beekmantown Group (Ordovician age).
REFERENCES: Flippo, H. N., Jr. [1974], Springs of Pennsylvania, Pennsylvania Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.
REMARKS: Boiling Springs, which has a median flow of 11,500 gallons per minute, ranks seventh in size of springs in the Commonwealth. It is one of the most picturesque springs in the Great Valley.
The origin of these springs is unique: the folded Cambrian limestones and dolomites of the Elbrook Formation have been injected by the near-vertical, thin diabase dike. This diabase is almost impervious and acts as a hydrologic barrier. At Boiling Springs the dike splits into two segments, so that the village is located in the interior apex of a "V" formed by the dikes. The direction of groundwater flow is to the north and east from the higher elevations on South Mountain. Groundwater becomes progressively confined between the two dikes until it "boils" forth from two main springs near the apex.
REFERENCES: Flippo, H. N., Jr. [1974], Springs of Pennsylvania, Pennsylvania Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.
Root, S. I. [1976], Engineering problems in areas of limestone springs, Pennsylvania Geology, v. 7, no. 2, p. 6-9.
REMARKS: A spire of quartzite (Antietam Formation, Cambrian age) in the shape of a chimney rises above the surrounding ridge line. The name of this topographic feature is also the name of the first-order U. S. Gelogical Survey triangulation station and bronze marder at this site.
REMARKS: A magnificent overlook and view of the Blue Ridge province. Outcrops of Weverton conglomerate (Cambrian age) show pebbles that have been elongated due to deformation.
REFERENCES: Freedman, Jacob [1967], Geology of a portion of the Mount Holly Springs quadrangle, Adams and Cumberland Counties, Pennsylvania, Pennsylvania Geological Survey, 4th ser., Progress Report 169, 66 p.
REMARKS: A group of three springs is the sixth largest in the Commonwealth, having a combined median flow of 12,000 gallons per minute. The springs issue from fractures in the Tomstown Dolomite (Cambrian age). The origin of the springs is probably due to a combination of rock composition and fracturing (both jointing and faulting).
REFERENCES: Flippo, H. N., Jr. [1974], Springs of Pennsylvania, Pennsylvania Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.
REMARKS: Hard, tough, weather-resistant spires of quartzite (Weverton Formation, Lower Cambrian age) are spectacular at this site, which is near the Appalachian Trail.
REMARKS: Abundant fossils occur in a Middle Ordovician limestone (Chambersburg Formation). This is one of the best fossil areas in this type of rock in Pennsylvania.
TOWNSHIP: CookeREMARKS: This magnificent pillar of rock rises over South Mountain and provides an exceptional view of Mountain Creek Valley and the surrounding highlands. Pole Steeple is a hard, light-gray quartzite (Montalto Member of the Harpers Formation, Cambrian age). Less resistant rocks in the valley to the north around Laurel Forge Pond are metarhyolite and dolomite. These two rock types were faulted upward against the quartzite, and, because they erode more rapidly than the quartzite, they now occupy a lower topographic position.
REFERENCES: Royer, D. W. [1981], Caledonia and Pine Grove Furnace State Parks, Cumberland, Adams, and Franklin Counties - Geologic features and iron ore industry, Pennsylvania Geological Survey, 4th ser., Park Guide 15, pamphlet.
Wilshusen, J. P. [1983], Geology of the Appalachian Trail in Pennsylvania, Pennsylvania Geological Survey, 4th ser., General Geology Report 74, 121 p.
PHOTO: © Michael Lane. "Looking northeast. There's a parking area located on the south side of the lake next to the trailhead. It's a short, steep, rocky walk to the top (about 3/4 of a mile, one way). It's also within 1/2 mile of the Appalachian Trail."
REMARKS: A balanced pinnacle about 15 feet high is a striking solitary feature of Sunset Rocks. Different rates of erosion have caused this hard, dense, light-gray, coarse-grained sandstone and quartzite (Weverton Formation, Cambrian age) to weather in relief against the surrounding rocks. Individual beds also may weather faster than others, causing the balanced pinnacle.
REFERENCES: Wilshusen, J. P. [1983], Geology of the Appalachian Trail in Pennsylvania, Pennsylvania Geological Survey, 4th ser., General Geology Report 74, 121 p.
REMARKS: An excellent view across the Great Valley to Blue Mountain. This is a pinnacled ridge of quartzite of the Antietam Formation (Cambrian age) crossed at Center Point Knob (317) by the Appalachian Trail.