Last update: 14-JAN-2012

Pennsylvania Geologic Features

This file is from various sources. Not sure what can be found anymore.

Columnar Jointed Volcanics
TOWNSHIP: Franklin
QUADRANGLE: Iron Springs
LOCATION: About 2.5 miles northeast of the village of South Mountain.

REMARKS: Well-preserved columnar joints in the Catoctin metarhyolite 
(Precambrian age) are exposed along the west wall of the dam and spillway. 
The reservoir serves as a water supply for the hospital at South Mountain. 
Unique columnar structures exposed here are about 20 feet high and as much 
as 2 feet wide, and have hexagonal and pentagonal sides. Tree cover behind 
the spillway wall is sufficiently thick during the summer months to 
completely hide this feature.

REFERENCE: Pennsylvania Geology (1969), Columnar jointing in South Mountain, 
v. 1, no. 2, p. 7.

Devils Den / Little Round Top / Round Top TOWNSHIP: Cumberland QUADRANGLE: Gettysburg LOCATION: Within the Gettysburg National Military Park. REMARKS: A mass of diabase boulders facing Little Round Top (336) and Round Top (337). Thousands of sightseers have climbed these rocks on the Gettysburg battlefield to look over the fields where Pickett's men charged on July 3, 1863. Very few of these Civil War buffs know that these geologic features that Generals Lee and Meade fought among are the outcrop of a diabase sill, called the Gettysburg sill. The sill intruded into the Triassic red sandstones and shales that floor the broad Gettysburg Valley 180 million years ago. Few have any idea of the extent to which the battle was influenced by the geology of the region. REFERENCE: Brown, Andrew (1962), Geology and the Gettysburg campaign, Pennsylvania Geological Survey, 4th ser., Educational Series 5, 15p.

The Narrows TOWNSHIP: Franklin QUADRANGLE: Arendtsville LOCATION: Two miles northwest of the Borough of Arendtsville. REMARKS: A water gap formed by Conewago Creek; has a macimum relief of 680 feet. Large and numerous outcrops of gray-green metarhyolite (Pre-cambrian age) dot the surface; note the flow structures and various sized porphyritic textures. REFERENCE: Shirk, W. R. (1978), The geology of south-central Pennsylvania, Guidebook, National Association of Geology Teachers, Eastern Section, Shippensburg State College, Shippensburg, Pennsylvania, 73p.

Cold Valley TOWNSHIP: Hampton QUADRANGLE: Glenshaw LOCATION: A steep-walled valley along Crouse Run, west of Hampton Cemetery and the village of Talley Cavey. REMARKS: The valley boeeom remains cold through much of the summer months. Narrow valley walls channel and trap winter air currents so that the valley bottom remains cool thoughout the year. The wildflower snow trillium (Trillium nivale) is found here as well as other plants normally found in more northern climates. Rocks exposed in the valley walls are sandstones, siltstones, and shales of the Glenshaw Formation of the Conemaugh Group (Pennsylvanian 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.

Crooked Creek TOWNSHIPS: Manor, Bethel, and Burrell QUADRANGLE: Leechburg LOCATION: At Crooked Creek State Park along Crooked Creek, a tributary of the Allegheny River. REMARKS: A series of closely spaced meanders five the creek its name. An exceptional set of meanders at this site is highly scenic.

Big Knob TOWNSHIP: New Sewickley QUADRANGLE: Baden LOCATION: Adjacent to PA Route 68, 1.9 miles south of Unionville. REMARKS: At elevation 1383 feet, this peak is the highest point in the county. Big Knob is an erosional remnant of the old plateau surface; the knob lies in the trough of a gently plunging syncline and is an excellent example of a "syncline mountain." Drainage from Big Knob is radial in pattern, and the hill is the result of the headward erosion of this drainage system that has left the youngest rocks standing high in relief above the surrounding terrain. The knob is capped by the Morgantown sandstone, the lowest resistant rock unit of the Cassleman Formation (Conemaugh Group); the Ames limestone crops out at an elevation of about 1260 feet and forms a bench around the hill at this elevation.

Blue Knob TOWNSHIP: Union QUADRANGLE: Blue Knob LOCATION: PA Route 869 at the village of Pavia; the summit and surrounding area are within Blue Knob State Park. REMARKS: The second highest peak (elevation 3146 feet above sea level) in Pennsylvania. The lookout tower at the summit has been removed, but number lookouts are provided throughout the park; a balanced rock is also present near the summit. At the base of the mountain gently dipping red siltstones and shales of the Catskill Formation (Devonian age) may be seen along the roads and trails. Near and at the summit of Blue Knob, outcrops of gray-green conglomerate of the same formation are found. The conglomerate is far more resistant to weathering than the shales and siltstones, and therefore remains as a peak (Blue Knob) above the surrounding countryside.

Hogback TOWNSHIP: West Providence QUADRANGLE: Everett East LOCATION: Along the Raystown Branch of the Juniata River; 4 miles northeast of Everett. REMARKS: A narrow sliver of red shale, siltstone, and sandstone (Catskill Formation, Devonian age) in a tight meander of the Raystown Branch of the Juniata River. These are classic examples of meanders and are the best in the Commonwealth.

Shaefer Overlook / The Kettle TOWNSHIP: King QUADRANGLE: New Enterprise LOCATION: On PA Route 869, approximately 4 miles west of New Enterprise and atop Dunning Mountain. REMARKS: A breathtaking view (looking west) of the Valley and Ridge province. A sign at this site reads, "Dedicated to Charles 'Pop' Shaefer, 'This beautiful spot is to collect our thoughts of God's great goodness, not the waste of man.'" The Kettle (269), in south Woodbury Township, is visible from a site on the east side of the mountain crest.

Blue Rocks Block Field TOWNSHIPS: Greenwich and Albany QUADRANGLE: Hamburg LOCATION: Two miles northwest of Lenhartsville. REMARKS: A long narrow "train" of angular blocks (often called a boulder field), about one-half mile long and ranging in width from 200 to 600 feet, on the southern slope of Blue Mountain. It was formed by solifluction or creep in the periglacial climate of the Wisconsinan glaciation, after which removal of fine-grained material occurred. Blue Rocks and adjacent rubble depostits closely resemble solifluction sheets in Alaska. REFERENCE: Potter, Noel, Jr., and Moss, J. H. (1968), Origin of the Blue Rocks Block Field and adjacent deposits, Berks County, Pennsylvania, Geological Society of America Bulletin, v. 79, p. 255-262.

Cushion Peak TOWNSHIP: South Heidelberg QUADRANGLE: Sinking Spring LOCATION: On the northern rim of South Mountain, 3.2 miles southwest of the Borough of Sinking Spring. REMARKS: The Hardyston Quartzite (Cambrian age) has been thrust faulted over the limestone valley at this site. This "rootless slice" of Hardyston Quartzite contains an isolated peak, Cushion Peak, rising more than 800 feet above the Great Valley to the north; an excellent view of the Great Valley from the peak. REFERENCE: MacLachlan, D. B., Buckwalter, T. V. and McLaughlin, D. B. (1975), Geology and mineral resources of the Sinking Spring 7 1/2-minute quadrangle, Berks and Lancaster Counties, Pennsylvania, Pennsylvania Geological Survey, 4th ser., Atlas 177d, 228 p.

Devils Hump / Owl Head / Pinnacle Point TOWNSHIP: Earl QUADRANGLE: Boyertown LOCATION: Two and two-tenths miles west of Boyertown on Fancy Hill. REMARKS: A basal conglomerate in the Hardyston Quartzite (Cambrian age) is so extremely hard and resistant to weathering that individual peaks stand topographically above the surrounding granite gneiss (Precambrian age); Devils Hump, Owl Head (325), and Pinnacle Point (326) are three of the highest. REFERENCES: Buckwalter, T. V. [1959], Pre-Cambrian geology, Boyertown quadrangle, Pennsylvania Geological Survey, 4th ser., Atlas 197, 15 p.

Hawk Mountain Lookouts / North Lookout / Dans Pulpit / South Lookout / Cobble / River of Rocks / Hemlock Heights / Owls Head TOWNSHIP: Albany (Berks County); East Brusnwick (Schuykill County) QUADRANGLE: New Ringold LOCATION: One and three-tenths miles east of Drehersville on Blue Mountain; the area is included in the Hawk Mountain Sanctuary, a privately maintained refuge. REMARKS: Several outstanding geologic features are present in the immediate area: the North Lookout (222) on Hawk Mountain and Dans Pulpit (223) on Blue Mountain are in East Brunswick Township, Schuylkill County; South Lookout (224), Cobble (225), River of Rocks (226), Hemlock Heights (227), and Owls Head (228) are in Albany Township, Berks County. Towering outcrops and joint blocks of the Tuscarora quartzite (Silurian age) are exposed. The North Lookout is a massive outcrop of Tuscarora sandstone, 1520 feet above sea level; from this site, one may view a truly majestic 70-mile vista of the Great Valley and Blue Mountain. South Lookout is 1340 feet above sea level. The River of Rocks, a boulder field formed during the Ice Age, is 1 mile long and several hundred feet wide. Dans Pulpit is formed from outcrops of the Tuscarora quartzite standing in vertical columns. They are spectacular, and the scenic view to the south across the Great Valley is magnificent. The Appalachian Trail is adjacent to these geologic features. The area has been designated a National Natural Landmark.

Mount Penn Scenic Lookout TOWNSHIP: Lower Alsace CITY: Reading QUADRANGLE: Reading LOCATION: Skyline Drive in the City of Reading and Lower Alsace Township. REMARKS: A scenic drive along the ridge of Mount Penn at an elevation of 800 to 1000+ feet. Along the drive are the Pagoda and a lookout tower, which provide an excellent view of the Reading Prong and Great Valley.

The Pinnacle TOWNSHIP: Albany QUADRANGLE: Hamburg LOCATION: Approximately 3.0 miles north of Lenhartsville on Blue Mountain. REMARKS: Outcrops of hard, resistant quartzite (Tuscarora Formation, Silurian age) are exposed at the apex of a tight fold in the mountains. Weathering has produced a "spire" of quartzite; an excellent view of the Great Valley.

Schuylkill Gap TOWNSHIP: West Brunswick (Scuylkill County); Tilden (Berks County) QUADRANGLE: Auburn LOCATION: One-half mile south of the center of the Borough of Port Clinton; 1.8 miles north of Interstate 78 and PA Route 61. REMARKS: An outstanding example of a water gap in Blue Mountain; an exceptional exposure of the quartzites of the Tuscarora Formation (Silurian age) and a major fault which causes this formation to repeat. REFERENCES: Burner, Roger, Weaver, Richard, and Wise, Donald [1958], Structure and stratigraphy of Kittatinny Ridge at Schuylkill Gap, Pennsylvania, Pennsylvania Academy of Science Proceedings, v. 32, p. 141-145.

Spitzenberg Hill TOWNSHIP: Albany QUADRANGLE: Kutztown LOCATION: Six-tenths mile east of the village of Greenawald and PA Route 143; 1.7 miles north of the village of Klinesville and Interstate 78. REMARKS: This small topographic hill has been the site of a raging geologic controversy for more than 40 years. The hill lies in the middle of the Martinsburg Shale (Ordovician age), but some geologists since 1934 have said that it is limestone conglomerate of Triassic age, a synclinal outlier of Triassic rocks. Today geologists have identified fossils (brachiopods and graptolites) that date the rocks as Late Ordovician; they are now thought to be part of the Juniata and Bald Eagle Formations. REFERENCES: Platt, L. B., Loring, R. B., Papaspyros, Athanasios, and others [1972], The Hamburg klippe reconsidered, American Journal of Science, v. 272, p. 305-318. Whitcomb, Lawrence [1942], Spitzenberg Conglomerate as a Triassic outlier in Pennsylvania, Geological Society of America Bulletin, v. 53, p. 755-764. Whitcomb, Lawrence and Engel, J. A. [1934], The probable Triassic age of the Spitzenberg Conglomerate, Berks County, Pennsylvania, Pennsylvania Academy of Science Proceedings, v. 8, p. 37-43.

Lake Arthur TOWNSHIPS: Muddy Creek, Brady, Franklin, and Worth QUADRANGLE: Prospect LOCATION: Lake Arthur, in Moraine State Park, is located12 miles west of Butler, near the U. S. Route 422 and Interstate 79 interchange. REMARKS: The lake occupies the site of a glacial lake that existed here over 10,000 years ago, when a continental glacier covered much of northwestern Pennsylvania. The glacial ice, whose eastern edge was at Harrisville and Slippery Rock, dammed the westward-flowing Slippery Rock and Muddy Creeks, forming lakes in their valleys; in the latter, Lake Arthur was formed. REFERENCES: Lytle, W. S. (1959), Field Trip C, Stop 1, Glacial Lake, in Guidebook, 24th Annual Field Conference of Pennsylvania Geologists, Pennsylvania Geological Survey, p. 67-69. __________ (1970), Moraine State Park, Pennsylvania Geological Survey, 4th ser., Park Guide 4.

West Liberty Esker TOWNSHIP: Worth QUADRANGLE: Slippery Rock LOCATION: Between West Liberty and Jacksonville. REMARKS: This 3-mile-long esker is probably the best remaining example of this type of glacial deposit in western Pennsylvania. The esker was formed during the close of the Wisconsonian glaciation, and is also known as the Miller Esker and West Liberty "Hogback." Eskers are ridge-shaped sand and gravel deposits formed during the melting of a glacier. The ridge form marks the trace of a glacial meltwater stream that is confined within the ice mass. Esker ridges are always associated with the stagnation phase of the glacial episodes. There are two major ways that the esker ridge can form: 1) in an ice tunnel along the base of or within the stagnated ice mass, and 2) as a meltwater channel deposit or crevasse filling on the surface of the ice. The surface expressions of the resulting types of eskers are quite similar. A ridge will be formed, it will be somewhat sinuous, and it will be composed primarily of gravel. The distinctive difference in the surface expression is that the crevasse-filling type will have a tendency to form angular bends and the long segments (i.e., the unbended segments) will be nearly parallel. The ridge formed in an ice tunnel will have more of a sinuous-meander pattern characterized by sweeping meander bends and a few straight-line segments. The internal composition will also differ. The tunnel esker will often have a till blanket draped over the top of the deposit. The till will be indicative of transportation within the ice, showing long-distant movement of material. A pseudoanticline draping of the sediment within the deposit is common. Ice-contact faulting may be present but is usually not extensively developed. The crevasse filling will have fluvial-type deposition to the surface. There may be some areas that have flow till incorporated into the deposit because supraglacial material flowed into the crevasse from the ice surface. Ice-contact faulting of the sediment is common because the sides of the deposit were held in place by the ice mass, and, when the ice melted away, faulting developed as the sides of the sedimentary mass were let down. The West Liberty Esker is believed to be a crevasse filling for the following reasons: 1) The existence of straight-line segments of the ridge connected by a sharp bend. 2) Glaciofluvial gravels are present across the whole ridge. 3) Numerous normal, ice-contact faults occur along the edge of the ridge. 4) No till blanket has been observed on the ridge.

Castle Rocks / Big Rock Spring / Sand Spring TOWNSHIP: Crawford QUADRANGLE: Carroll LOCATION: Approximately 2 miles south of Rauchtown on PA Route 880; 2.5 miles north of Interstate 80; within Ravensburg State Park. REMARKS: A scenic gorge along Rauchtown Creek contains spires of rock (Bald Eagle conglomerate, Ordovician age) forming the feature called "Castle Rocks." Big Rock Spring (202) and Sand Spring (203) are nearby. 063. Hyner View TOWNSHIP: Chapman QUADRANGLES: Glen Union and Renovo East LOCATION: Approximately 6.5 miles east of Renovo and 1.1 miles southeast of the village of Hyner on PA Route 120; part of Hyner Run State Park. REMARKS: A spectacular scenic lookout on Hyner Mountain; the scene is an overview of the West Branch of the Susquehanna River and the Allegheny High Plateau. This lookout is perched on a cliff edge more than 1300 feet above the Susquehanna River. Hyner View is ranked as one of the most outstanding scenic views in the United States. Excellent exposures of sandstone, shale, and conglomerate of the Catskill Formation (Devonian age) are seen along the road winding from the Hyner Run State Park office to the lookout; an unusual Catskill "breccia" bed is exposed at the second bend of the road below the lookout. LINKS: Hyner Overlook page by John Way. Hyner Run State Park

The Bunk / Oxbow Bend TOWNSHIP: Leidy QUADRANGLE: Hammersley Fork LOCATION: Along Kettle Creek, 1 mile south of the village of Hammersley Fork and PA Route 144. REMARKS: An ancient meander of Kettle Creek eroded the land within the meander into the shape of a built-in bed or bunk. The bend area of the meander resembles an oxbow and is known as Oxbow Bend (107).

Renovo View TOWNSHIP: Chapman QUADRANGLE: Renovo East LOCATION: Approximately 0.5 mile north of the Borough of Renovo and PA Route 120. REMARKS: A scenic overlook; view of the West Branch of the Susquehanna River and the Allegheny High Plateau. This overlook is perched on a cliff more than 900 feet above the river. Exposures of sandstone, shale, and conglomerate of the Catskill Formation (Devonian age) are seen along the dirt road winding from the borough to the lookout.

Seven Spring / Ruhl Spring TOWNSHIP: Logan QUADRANGLE: Millheim LOCATION: At the U. S. Bureau of Fisheries, Lamar National Fish Hatchery on Fishing Creek; approximately 2.2 miles west of Tylersville and PA Route 880. REMARKS: Seven Spring and Ruhl Spring (267) together make up the second largest spring system in Pennsylvania, having a flow of 14,000 gallons per minute. These springs issue from enlarged fracture openings in the Nealmont Limestone of Ordovician age. REFERENCES: Flippo, H. N., Jr. (1974), Springs of Pennsylvania, Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.

Sulphur Spring BOROUGH: Loganton QUADRANGLE: Loganton LOCATION: On the Green Township-Loganton Borough boundary, one-half mile south of Interstate 80, exit 27 (mile 185). REMARKS: A sulfur spring located in a water gap in Sugar Valley Mountain. The spring is emanating from conglomerate of the Bald Eagle Formation (Ordovician age). A bright yellow coating of native sulfur is present on the walls of the spring opening. REFERENCES: Bolles, W. H. , and Geyer, A. R. (1975), PA Interstate 80 - geologic guide, Pennsylvania Department of Education.

Tylersville Spring TOWNSHIP: Logan QUADRANGLE: Millheim LOCATION: Near the head of Fishing Creek, about one-half mile northeast of the village of Tylersville; approximately 600 feet east of PA Route 880. REMARKS: The fourth largest spring in Pennsylvania, having a median flow of 13,000 gallons per minute. The spring rises from fractures in the limestone of the Nealmont Formation (Ordovician age). REFERENCES: Flippo, H. N., Jr. (1974), Springs of Pennsylvania, Department of Environmental Resources, Office of Resources Management, Water Resources Bulletin 10, 46 p.

Conneaut LakeTOWNSHIP: Sadsbury QUADRANGLES: Conneaut Lake and Harmonsburg LOCATION: Immediately north of the Borough of Conneaut Lake and U. S. Route 322. REMARKS: Pennsylvania's largest lake; 938 acres.

Conneaut Lake Kame TOWNSHIP: Sadsbury QUADRANGLE: Conneaut Lake LOCATION: One mile east of Conneaut Lake. REMARKS: One of the largest kames in the state; this glacial deposit marks the location of a depression filled with sand and gravel in or at the margin of stagnant ice as the glacier melted. At present a portion of the kame is being quarried for gravel. REFERENCES: Shepps, V. C. [1962], Pennsylvania and the Ice Age, Pennsylvania Geological Survey, 4th ser., Educational Series 6, 33 p.

Conneaut Marsh TOWNSHIPS: Union and Greenwood QUADRANGLES: Geneva LOCATION: Adjacent to the Conneaut Outlet, the southern outlet to Conneaut Lake; about 4.5 miles south of Meadville; within State Game Lands No. 213. REMARKS: One of the largest marshes in Pennsylvania, contained in an ancient stream channel that was filled with glacial till during the last glaciation in Pennsylvania. The American bald eagle nests in the marsh and the rare bog turtle has been reported. 005. Rock Creek Ravine, at Custards in Greenwood Township, contains a series of scenic waterfalls.

Dead-Ice Terminal Moraine TOWNSHIP: Wayne QUADRANGLE: Sugar Lake LOCATION: Southeastern corner of the county, immediately northwest of the Crawford-Venango County line; the moraine parallels the county line in a northeaster-southwest direction. REMARKS: The most outstanding topographic example of a terminal moraine in western Pennsylvania. This moraine marks a "dead" or stagnant position of the ice front during the Great Ice Age in Pennsylvania. The topography on the moraine is particularly hummocky due to the presence of unsorted rock materials that were pushed or carried there by the glacier.

Big Spring TOWNSHIP: West Pennsboro QUADRANGLE: Newville LOCATION: The head of Big Spring Creek in the village of Big Spring; approximately 3 miles south of the Borough of Newville. The spring is owned and used by the Pennsylvania Fish Commission for the Big Spring Trout Hatchery. 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.

Boiling Springs TOWNSHIP: South Middleton QUADRANGLE: Carlisle LOCATION: At the head of a small lake in the village of Boiling Springs; the site of a community park. 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.

Chimney Rocks TOWNSHIP: Penn QUADRANGLE: Dickinson LOCATION: In the southwestern corner of the township, approximately 4 miles north of the Cumberland-Adams County line and Pa. Route 233. 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.

Hammonds Rocks TOWNSHIP: Dickinson QUADRANGLE: Mount Holly Springs LOCATION: Four and four-tenths southwest of Mount Holly Springs on the crest of South Mountain. 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.

Huntsdale Hatchery Springs TOWNSHIP: Penn QUADRANGLE: Dickinson LOCATION: In the village of Huntsdale, approximately 9 miles southwest of Carlisle. The Pennsylvania Fish Commission owns and uses these springs for its Huntsdale Hatchery. 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.

Lewis Rocks TOWNSHIP: Southampton QUADRANGLE: Dickinson LOCATION: Approximately 13 miles north of Caledonia and U. S. Route 30; on Big Hill in South Mountain, within Michaux State Forest. REMARKS: Hard, tough, weather-resistant spires of quartzite (Weverton Formation, Lower Cambrian age) are spectacular at this site, which is near the Appalachian Trail.

Logan School Fossil Site TOWNSHIP: West Pennsboro QUADRANGLE: Plainfield LOCATION: North of the Pennsylvania Turnpike at Logan School; PRIVATE PROPERTY, NO TRESPASSING. 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.

Pole Steeple TOWNSHIP: Cooke QUADRANGLE: Dickinson LOCATION: About 2 miles east of the village of Pine Grove Furnace, 0.3 mile north of the Appalachian Trail and 0.4 mile south of Laurel Forge Pond and Pine Grove Furnace State Park. REMARKS: 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."

Sunset Rocks TOWNSHIP: Cooke QUADRANGLE: Dickinson LOCATION: Little Rocky Ridge, about 1 mile west of Pine Grove Furnace State Park. 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.

White Rocks / Center Point Knob TOWNSHIP: Monroe QUADRANGLE: Dillsburg LOCATION: Three and eight-tenths miles west of Dillsburg on the north rim of South Mountain. 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.

Devils Backbone TOWNSHIP: Girard QUADRANGLE: Albion LOCATION: About 3.2 miles southeast of Girard along Little Elk Creek. REMARKS: The shape of the land within a series of meanders in Little Elk Creek resembles a "backbone"; a unique topographic feature created by stream erosion.

rumlins TOWNSHIP: Venango QUADRANGLE: Wattsburg LOCATION: Two miles northeast of Wattsburg along Macedonia Road; near State Game Lands No. 191. REMARKS: Drumlins, very common to the glaciated northwestern area of Pennsylvania, are low, smoothly rounded, elongate hills, mounds, or ridges of compact glacial till, built under the margin of the ice and shaped by its flow, or carved out of the older moraine by readvancing ice. The drumlin's longer axis is parallel to the direction of ice movement; the drumlin has a blunt nose pointing in the direction from which the ice approached, and gentler slope tapering in the opposite direction. Drumlins at this site are almost perfect textbook examples.

Presque Isle TOWNSHIP: Millcreek QUADRANGLE: Erie North LOCATION: Presque Isle State Park; along the southern shore of Lake Erie. REMARKS: Presque Isle is a relatively recent geologic feature of glacial origin, having developed less than 13,000 years ago, after the final retreat of glacial ice from northwestern Pennsylvania. The peninsula, approximately 6 miles long, is composed of sand deposits brought into the area from the west by lake currents. Within record, except for diminishments in the periods 1790-1818 and 1837-1866, Presque Isle has grown so that presently the neck is about three times longer, the exposed land area three to four times greater, and the overall reach of the feature nearly three times greater than in 1790. Over the years there has been a movement and growth of the entire peninsula in a northeasterly direction, the direction of the lake current, and the recession of the lakeside beaches at the southwest end. The northeastward growth of Presque Isle created small ponds of water of various ages. This situation provides a unique opportunity for the scientific study of the plant and animal life in and around these ponds. Therefore, in addition to being a scenic geological feature, the biological environment of Presque Isle is of considerable scientific importance. The site is also of historical importance because it is associated with Perry's great victory of the Battle of Lake Erie in the War of 1812. It is a registered National Natural Landmark. REFERENCES: Hough, J. L. [1958], Geology of the Great Lakes, University of Illinois Press, Urbana, Illinois, 313 p. Tomikel, J. C. and Shepps, V. C. [1967], The geography and geology of Erie County, Pennsylvania Geological Survey, 4th ser., Information Circular 56, 64p. U. S. Army Corps of Engineers [1973], Revised draft, Environmental Impact Statement on the Cooperative Beach Erosion Project at Presque Isle, Pennsylvania [Erie, Pennsylvania], Buffalo District, p. 45.

Titus Bog TOWNSHIP: Amity QUADRANGLE: Union City LOCATION: Approximately 20 miles southeast of Erie; 4.5 miles south of the Borough of Wattsburg. REMARKS: A marl bog that contains an acid sphagnum mat surface; this bog and the nearby Wattsburg Bog are excellent examples of sphagnum bogs surrounded by a well-developed swamp forest; both bogs are registered National Natural Landmarks.

Beartown Rocks / Stahlman Roundtop TOWNSHIP: Heath QUADRANGLE: Sigel LOCATION: About 3.5 miles northeast of the village of Sigel; 1.5 miles east of PA Route 949; within Kittanning State Forest and near Clear Creek State Park. REMARKS: A "rock city" (large blocks of rock that have weathered extensively along joint cracks, producing interconnected passageways, tunnels, and crevices); blocks of standstone and conglomerate of the Pottsville Group (Pennsylvanian age). The site is immediately north of the Kellersburg anticlinal axis and is surrounded by one of the Commonwealth's major natural gas fields. Stahlman Roundtop (25), 2 miles south of Beartown Rocks, is a weathered remnant of basal sandstones of the Allegheny Group

Black Rock TOWNSHIPS: Colerain QUADRANGLE: Kirkwood LOCATION: At the intersection of Pa. Route 472 and the West Branch of Octoraro Creek; 1.9 miles northwest of Kirkwood. REMARKS: Massive outcrops of albite-chlorite schist of the Wissahickon Formation (Precambrian (?) age) in a narrow gorge of the West Branch produce a highly scenic setting. A public spring marked "Black Rock" is nearby.

Chickies Rock TOWNSHIPS: West Hempfield QUADRANGLE: Columbia West LOCATION: One mile north of the Borough of Columbia. REMARKS: A magnificent anticline of Lower Cambrian Chickies Quartzite is exposed along the Susquehanna River at the west end of Chickies Ridge. This is also the site of a fine overlook and picnic area atop the anticline. The Chickies Quartzite contains rare animal borings, or tubes, called "scolithus tubes"; these were once thought to be a Cambrian-age marine worm, Scolithus.

Conowingo Islands / Upper Bear Island / Lower Bear Island / Piney Island / Brushy Island / Peavine / Wildcat / Crow Islands / Deepwater / Turkey Islands / Little Chestnut / Wolf / Sicily / Beach Islands / Mount Johnson Island TOWNSHIPS: Martic and Drumore (Lancaster County); Lower Chanceford (York County) QUADRANGLE: Holtwood LOCATION: South of the Holtwood Dam on the lower Susquehanna River; south of the Pa. Route 372 bridge. REMARKS: South of the Holtwood Dam there are over 60 islands. In contrast to the others in the river, which are alluvial in nature, the Conowingo Islands are erosional remnants of the metamorphic rocks (schists and gneisses) of southern Lancaster County. This group of islands represents one of the most scenic areas of the state. The larger islands are: 356. Upper Bear Island: the largest of the group and the most primitive; has ridges of bedrock. 357. Lower Bear Island: second in size; the northern third is very rocky and has sheer-walled old channels, and ponds and marshes. 358. Piney Island: the northernmost of the group and immediately south of the Holtwood Dam; about half of the island is exposed rock. 359. Brushy Island: this and the cluster of islands immediately west of Piney Island are aptly named; very brushy; contains large exposures of Wissahickon Schist (Precambrian (?) age). 360. Peavine, 361. Wildcat, and 362. Crow Islands : these islands and lesser ones total about 35 acres and are north and west of Upper Bear Island and immediately downstream from the Norman Wood Bridge; they are low, rocky islands. 363. Deepwater and 364. Turkey Islands: two small areas east of the Bear Islands and very close to the York County Shoreline. 365. Little Chestnut, 366. Wolf, 367. Sicily, and 368. Beach Islands : a scattered cluster near Big Chestnut and Hennery Islands; these small islands are especially scenic because of their spectacular high cliffs. 369. Mount Johnson Island: the southernmost island of the group; it towers 200 feet above the river and is very rugged.

Eagle Rock TOWNSHIP: Elizabeth QUADRANGLE: Lititz LOCATION: Approximately 1.4 miles northwest of the village of Brickerville (intersection of PA Route 501 and U. S. Route 322); along the Horseshoe Trail at elevation 960 feet, between Furnace Creek and Hammer Creek; on Furnace Hills. REMARKS: Outcrops of quartz conglomerate of the Hammer Creek Formation (Triassic age); one outcrop has weathered unevenly and now resembles the shape of an eagle. Potholes in the Susquehanna River / Conewago Falls TOWNSHIP: Conoy QUADRANGLE: York Haven LOCATION: Conewago Falls in the Susquehanna River opposite the village of Falmouth. REMARKS: A series of extremely large potholes in diabase (Triassic age) in the bed of the Susquehanna River; visible yearly at low water levels. REFERENCES: Beck, H. H. [1948], Prolonged drouth uncovers geologic phenomenon, Pennsylvania Department of Internal Affairs Bulletin, v. 16, no. 2, p. 3-6. ___________ [1948], The pot holes of Conewago Falls, Pennsylvania Academy of Science Proceedings, v. 22, p. 127-230. Myers, R. E. [1953], The Conewago pot holes of the Susquehanna River, Pennsylvania Angler, v. 22, no. 10, p. 6-9, 25-27.

Quakertown Falls TOWNSHIP: Mahoning QUADRANGLE: Campbell, Ohio-Pennsylvania LOCATION: One-half mile east of the Ohio-Pennsylvania border and about 0.7 mile northwest of the village of Hillsville. REMARKS: The falls are best viewed from near the Pittsburgh and Lake Erie Railroad tracks at the junction with U. S. Route 224. A 50-foot waterfall and a steep-walled valley mark the path of Quakertown Run flowing into the Mahoning River. Waterfalls of this magnitude are very rare in western Pennsylvania. I. C. White wrote the following in 1879 (p. 194 in reference below): "The run having leaped by a simgle bound into a deep and narrow cañon, bordered on either side by immense vertical and overhanging cliffs of sandstone, passes on down through the same amid the wildest scenery. This locality is a noted resort for picnic parties, since in the deep and narrow recesses of the minature canñon are many attractive nooks where the meridian sun never shines." The Upper Connoquenessing sandstone (Pottsville Group, Pennsylvanian age) forms the cliff rock of the falls. This sandstone is hard, coarse grained, massive, and white. Immediately under the sandstone is a foot-thick coal named the Quakertown coal for this locality. Very neat and ornate initials and the date '77 are carved into the rocks at the falls I. C. White studied the geology of this area in the summer of 1877, and he and his assistants may have been responsible for these carvings. REFERENCES: White, I. C. (1879), The geology Lawrence County, Pennsylvania Geological Survey, 2nd ser., Report of Progress 1877, v. QQ, 336 p.

Slippery Rock Creek Gorge / Spillway Falls / Muddy Creek Falls / Slippery Rock TOWNSHIP: Slippery Rock and Perry QUADRANGLE: Portersville LOCATION: Immediately west of the Lawrence-Butler County line near Portersville on U. S. Route 19. REMARKS: The striking scenery of the deep gorge of Slippery Rock Creek flowing through McConnells Mill State Park is the result of the glaciation of this area several tens of thousands of years ago, the park and gorge extend more than 4 miles in length. At Spillway Falls, a large volume of water plunged over the rim of the Homewood Sandstone Member of the Curwensville Formation (Pottsville Group, Pennsylvanian age) with enough energy to quickly enlarge and deepen the gorge. As the ice retreated, more spillways were opened. One of these north of Rose Point, Muddy Creek Falls (19), marks the last discharge channel from glacial Lake Arthur. Here Muddy Creek valley hangs above Slippery Rock Creek; the stream plunges about 100 feet over a very scenic falls. The Slippery Rock, which gave its name to the stream, a town, an oil field, an oil sand, a college, and a local football team, is a slab of Homewood sandstone along the east bank of the creek opposite Camp Allegheny. The rock is very slippery due to an oil seep, which occurs at the point where the stream was forded on foot and horseback by Indians and early settlers. Slippery Rock Creek Gorge, over 400 feet in depth, has a wealth of rocky cliffs, hanging valleys, and waterfalls. It is a registered National Natural Landmark.

Chinese Wall TOWNSHIP: Cold Spring QUADRANGLE: Tower City LOCATION: Included within Pennsylvania State Game Lands No. 211 on the crest of Sharp Mountain. REMARKS: A spectacular "wall" of outcrop of Sharp Mountain quartz-pebble conglomerate (Pottsville Group, Pennsylvanian age). The "wall" has also been known as High Rocks and Boxcar Rocks.

Cornwall Mine BOROUGH: Cornwall QUADRANGLE: Lebanon LOCATION: Between Cornwall and Miners Village, about 5 miles south of the city of Lebanon. REMARKS: An igneous, diabase layer of Triassic age intruded a sequence of limestone layers. Iron-rich solutions replaced the limestone bedrock and deposited a large iron ore body that had a wide variety of minerals. Mined from 1742 to 1973, it was the oldest continuously operated mine in the United States. The mine provided cannon shot and cannons for the Revolutionary War. REFERENCES: Gray, Carlyle, and Lapham, D. M. [1961], Guide to the geology of Cornwall, Pennsylvania, Pennsylvania Geological Survey, 4th ser., General Geology Report 35, 18 p. Lapham, D. M. [1972], Cornwall: the end of an era, Pennsylvania Geology, v. 3, no. 5, p. 2-5. Lapham, D. M., and Gray, Carlyle [1973], Geology and origin of the Triassic magnetite deposit and diabase at Cornwall, Pennsylvania, Pennsylvania Geological Survey, 4th ser., Mineral Resource Report 56, 343 p.

Dinosaur Rock TOWNSHIP: South Londonderry QUADRANGLE: Elizabethtown LOCATION: Approximately 0.75 mile south of Colebrook along PA Route 241; on State Game Lands No. 145 REMARKS: A local name applied to an erosional remnant of a Triassic-Jurassic diabase sheet. The diabase of this large intrusion is a medium- to coarse-grained, dark-gray rock having ophitic texture. The rock in the outcrop is very massive and usually weathers into large spheroidal boulders.

Eagle Peak TOWNSHIP: Millcreek QUADRANGLE: Womelsdorf LOCATION: Approximately 0.3 mile west of the Lebanon-Berks County line; 1.7 miles southeast of the village of Newmanstown; about 2000 feet northeast of Sheridan Road. REMARKS: The hard, resistant quartzite and conglomerate of the Hardyston Formation (Cambrian age) underlie this feature and account for its high relief (1300 feet above sea level). Numerous exposures of quartzite on the summit have weathered into various shapes.

Schaefferstown (Walnut) Spring BOROUGH: Schaefferstown QUADRANGLE: Richland LOCATION: Along south Market Street in borough of Schaefferstown, which is about 7.5 miles southeast of Lebanon and 17 miles north of Lancaster. N 40° 17.709' - W 076° 17.619' REMARKS: Schaefferstown Spring issues from the limestone conglomerate of the Hammer Creek Formation (Triassic age). The yield is usually less than 10 gallons per minute. This spring was deeded from Alexander Schaeffer to the residents of Market Street on July 16, 1763. The water is now piped from the spring to a fountain near the spring and to two fountains on Market Street. The water flows by gravity from the spring in Fountain Park to the fountains. It is the oldest chartered waterworks in the United States. REFERENCES: Gray, Carlyle, Geyer, A. R., and McLaughlin, D. B. (1958), Geology of the Richland quadrangle, Pennsylvania Geological Survey, 4th ser., Atlas 167, scale 1:24,000. Thomas R. Brendle Museum of Historic Schaefferstown, Inc., Schaefferstown, Pa.

Swatara Gap Fossil Site TOWNSHIP: Union QUADRANGLE: Indiantown Gap LOCATION: One mile north of Lickdale at Swatara Gap in Blue Mountain; on the west side of Swatara Creek directly beneath the Interstate 81 bridge over the creek. REMARKS: An outcrop of Ordovician shale containing the largest abundance of the trilobite Cryptolithus in Pennsylvania; also contains excellent specimens of the rare Ordovician starfish Hallaster. REFERENCES: Hoskins, D. M. [1969], Fossil collecting in Pennsylvania, Pennsylvania Department of Geological Survey, 4th ser., General Geology Report 40, 2nd printing, revised 126 p. Cramer, H. R. [1957], Ordovician starfish from the Martinsburg Shale, Swatara Gap, Pennsylvania, Journal of Paleontology, v. 31, p. 903-907.

Indian God Rock TOWNSHIP: Rockland QUADRANGLE: Kennerdell LOCATION: On the east bank of the Allegheny River, 2 miles north of the village of Brandon, near the 115-mile post on the Penn Central Railroad Tracks. REMARKS: A large outcrop of sandstone (Cuyahoga Group, Mississippian age) forms a sloping, flat bedding surface facing the river; early Indians carved figures on the face of the rock. Carvings represent their tribes, birds, and animals of the region. REFERENCES: Swauger, J. L. (1977), The Indian God Rock Petroglyph Site 36VE36, Pennsylvania Archeologist, v. 47, no. 1, p 1-13.

Oil Seeps TOWNSHIP: Oil Creek and Cherrytree QUADRANGLE: Titusville South LOCATION: Along Oil Creek between Oil City and Titusville; about 2 miles east of PA Route 8. REMARKS: Oil from seeps along Oil Creek was collected by the Indians and early settlers to be used as medicine. An oil spring was first described in 1753. In 1859 the Drake Well along Oil Creek was the world's first well drilled for oil. A replica of the Drake Well may be seen at Drake Well State Park, Titusville. Large and numerous outcrops of flat-lying greenish-gray siltstones (Riceville Formation, Late Devonian age) are present near Petroleum Center. REFERENCES: Pennsylvania Bureau of Statistics, Pennsylvania Bureau of Topographic and Geologic Survey, and the Pennsylvania State University (1944), Pennsylvania's Mineral Heritage, Pennsylvania Department of Internal Affairs, Harrisburg, 248 p. Pennsylvania Geological Survey (1959), Field Trip B, Bedrock and Oil Geology of Northwestern Pennsylvania and the Great Oildorado, in Guidebook, 24th Annual Field Conference of Pennsylvania Geologists, Pennsylvania Geological Survey, p. 36-58.

Warren Pikes Rocks / Lottsville Rock City / Nuttles Rocks / Brooks Rocks / Baker Rocks TOWNSHIP: Sugar Grove QUADRANGLE: Lottsville LOCATION: About 2.5 miles northeast of U. S. Route 6 near the village of Wrightsville. REMARKS: The site of a "rock city" on the ridge between Little Brokenstraw and Stillwater Creeks; the rocks rise to an elevation of 1980 feet above sea level. Rock walls of conglomerate rise about 30 feet in height and weather into fantastic profiles. The rock is a massive conglomerate known as the Sharon Formation (basal Pottsville Group. Pennsylvanian age) that contains layers of clear to white, coarse pebbles, some as large as chicken eggs, and has little to no sand matrix. John F. Carll in 1880 wrote about the site (p. 23 in reference below): "It presents mural exposures on all sides, and looks in the distance, whatever point of perspective may be chosen, like the ruins of some Cyclopean structure built by a pre-historic race." Similar "rock cities," Lottsville Rock City (12), Nuttles Rocks (13), Brooks Rocks (14), and Baker Rocks (15), occur nearby, but Pikes Rocks is the largest and most spectacular. REFERENCES: Carll, J. F. (1880), The geology of the oil regions of Warren, Venango, Clarion, and Butler Counties, Pennsylvania Geological Survey, 2nd ser., Report III, p. 23-33.

Tamarack Swamp TOWNSHIP: Columbus QUADRANGLE: Columbus LOCATION: Approximately 27 miles southeast of Erie and 4 miles north of the village of Columbus, Warren County; included within State Game Lands No. 197 on the Pennsylvania-New York border. REMARKS: A wide, deeply cut channel of Brokenstraw Creek was dammed during the Great Ice Age in Pennsylvania by a kame moraine during the retreat of the ice. This moraine caused a reversal in drainage direction and the eventual abandonment of the channel. Impervious clays and silts in this ancient channelway underlie Tamarack Swamp and are part of its origin. Poor drainage and great accumulations of organic matter have produced the bog, which is the finest example of a northern bog in Pennsylvania. The swamp is a registered National Natural Landmark.

Westmoreland TOWNSHIP: Cook QUADRANGLE: Bakersville LOCATION: About 3 miles south of U. S. Route 30 in Forbes State Forest; 1.5 miles west of the village of Laurel Summit along the Laurel Summit Road. REMARKS: The topographic crest of the Laurel Hill and the gelogical structural axis of the Laurel Hill anticline. Sandstone outcrops of the Allegheny Group (Pennsylvanian age) are exposed through weathering; there is a scenic view from the rim of the mountain. The name was applied to this feature because forest growth was slow to develop on this dry, rocky site. Strange sounds, similar to a swarm of bees, are peculiar to this knob; these sounds are attributed to traffic on the Pennsylvania Turnpike, located about 0.8 mile to the south.

Bear Rocks TOWNSHIPS: Derry and Fairfield QUADRANGLE: Bolivar LOCATION: On the crest of Chestnut Ridge about 8 miles west of New Florence; north of Bear Pond Hollow. REMARKS: Hard, resistant sandstone of the Connequenessing Formation (Pottsville Group, Pennsylvanian age) caps the elongated knobs on the crest of Chestnut Ridge; approximately 2 acres of weathered sandstone crops out. Joints in the sandstone that have been enlarged by weathering form a miniature "rock city"; very scenic. REFERENCES: Shaffner, M. N. [1958], Geology and mineral resources of the New Florence quadrangle, Pennsylvania, Pennsylvania Geological Survey, 4th ser., Atlas 57, 165 p.

Conemaugh Gorge TOWNSHIPS: West Taylor and Lower Yoder (Cambria County); St. Clair (Westmoreland County); East Wheatfield (Indiana County) QUADRANGLES: Vintondale and Johnstown LOCATION: Three miles northwest of the junction of the Little Conemaugh River and Stony Creek in Johnstown; PA Routes 403 and 56 parallel the Conemaugh River through the gorge. REMARKS: The Conemaugh River has eroded flat-lying sandstones, siltstones, and shales to form a magnificent gorge several miles in length. The topographic crest of the gorge (Laurel Hill) corresponds almost exactly in position to the Laurel Hill anticlinal axis. Massive sandstones of the Pottsville Group (Pennsylvanian age) form the rim, whereas softer, sandy shales of the Oswayo Formation (Devonian age) are exposed at the base. The geologic record of hundreds of millions of years is recorded in the rocks at this site. Where the crest of the ridge is formed by the massive and resistant sandstones of the Pottsville Group, the land is forested and relatively unpopulated. Laurel Hill is an excellent example of the influence of the rocks on man's activities; the ridge is covered with massive sandstone boulders and is practically uninhabited. REFERENCES: Phalen, W. C. [1910], Johnstown, PA, U. S. Geological Survey Atlas, Folio 174, 16 p.

Conemaugh Water Gap TOWNSHIPS: Fairfield (Westmoreland County); Burrell (Indiana County) QUADRANGLE: Bolivar LOCATION: About 1.7 miles west of the Borough of Bolivar where the Conemaugh River flows through Chestnut Ridge. REMARKS: An extremely scenic water gap eroded by the Conemaugh River through Chestnut Ridge; the topographic crest of the Chestnut Ridge coincides with the axis of the Chestnut Ridge anticline. Massive sandstones of the Pottsville Group (Pennsylvanian age) form the rim, whereas softer, sandy shales of the Oswayo Formation (Devonian age) are exposed at the base. The geologic record of hundreds of millions of years is recorded in the exposed rocks. REFERENCES: Shaffner, M. N. [1958], Geological and mineral resources of the New Florence quadrangle, Pennsylvania, Pennsylvania Geological Survey, 4th ser., Atlas 57, 165 p.

Loyalhanna Gorge / Buttermilk Falls TOWNSHIPS: Ligonier and Unity QUADRANGLE: Derry LOCATION: Three miles southeast of Latrobe; U. S. Route 30 parallels Layalhanna Creek in the gorge. REMARKS: A 3-mile-long gorge cut by Loyalhanna Creek through Chestnut Ridge; elevations range from 1040 feet at stream level to above 1900 feet on the rim. The river gradient drops about 100 feet in 3 miles and there are sections of boulder-stream rapids (Buttermilk Falls (128) is the largest and most spectacular). The topographic crest of the gorge (Chestnut Ridge) corresponds almost exactly in position to the axis of the Chestnut Ridge anticline. Massive sandstones of the Pottsville Group (Pennsylvanian age) form the rim, whereas softer, sandy shales of the Oswayo Formation (Devonian age) are exposed at the base. The geologic record of hundreds of millions of years is recorded in the rocks of this gorge. REFERENCES: Campbell, M. R. [1904], Latrobe, PA, U. S. Geological Survey Atlas, Folio 110, 15 p.

90-Foot Rocks / Adams Falls / Grove Run Spring / Flat Rock / Wolf Rocks / Beam Rocks (Somerset County) TOWNSHIP: Cook QUADRANGLE: Ligonier LOCATION: Within the gorge of Linn Run; adjacent to Linn Run State Park; 6 miles south of the Borough of Ligonier; on the west flank of Laurel Hill. REMARKS: Outcrops of sandstone of the Allegheny Group (Pennsylvanian age) form a cliff at this site; the view of Linn Run gorge and the Ligonier highlands is excellent. Nearby in the gorge, Adams Falls (131), Grove Run Spring (132), Flat Rock (133), and Wolf Rocks (134) are notable geologic features. Sandstones of the Pottsville Group (Pennsylvanian age) form Wolf Rocks; examples of joint blocks, frost wedging, and exfoliation are common along the trail to, and at, this site; a scenic overlook similar to that at 90-Foot Rocks is present. A little more than 2 miles east of Wolf Rocks and about 2000 feet east of Laurel Summit Road, Beam Rocks (135) (Somerset County, Lincoln Township) and vista are very similar to 90-Foot Rocks, geologically and topographically.

York County Stone Head TOWNSHIP: Franklin QUADRANGLE: Dillsburg LOCATION: About 4 miles southwest of the Borough of Dillsburg; 2 miles northeast of the junction York, Cumberland, and Adams Counties. REMARKS: An outcrop of quartzite of the Antietam Formation (Cambrian age) has weathered to a shape resembling a head. Lookout (314) on Long Mountain (Cumberland County, South Middleton Township) is a nearby similar outcrop (not similar in shape) along the Appalachian Trail.

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