ABSTRACT With waterfalls and the deepest gorge in Pennsylvania, Ohiopyle State Park provides opportunities to observe a variety of habitats and three-dimensional (3-D) exposures of the Pennsylvanian sandstone most responsible for shaping Laurel Highlands landscapes. Evidence for the relationship between bedrock, ancient climates, and the landscape can be observed at some of the most scenic natural features of the park: Baughman Rock Overlook, Cucumber Falls, Ohiopyle Falls, Meadow Run Waterslide and Cascades, and Youghiogheny River Entrance Rapid. Channel azimuths and lateral variations in thickness of upper Pottsville fluvial/deltaic sandstone suggest that deposition was influenced by deformation of this part of the Allegheny Plateau during the Alleghanian orogeny. Geologic features of Pottsville sandstone outcrops include a 10-m- (~33-ft-) long Lepidodendron fossil and a 3-D exposure of a meter-high Pennsylvanian subaqueous sand dune and scour pit. Cosmogenic age dating has indicated very slow erosion of hard sandstone in an upland location at Turtlehead Rock and informed estimation of Pleistocene/Holocene waterfall retreat rates of Ohiopyle and Cucumber Falls. Bedrock exposures supporting scour habitats along the Youghiogheny River occur only in a limited area of Youghiogheny Gorge where knickpoint migration and bedrock erosion were relatively recent. Geologic factors, including locations of major tributaries, development of bars that constrict river flow, and proximity of Homewood sandstone outcrops as sources of boulder obstacles in the river, contributed to the class, location, and nature of whitewater rapids in the lower Youghiogheny River.

ABSTRACT Fallingwater is a UNESCO World Heritage Site that showcases a unique organic architectural design by Frank Lloyd Wright. Rising from bedrock in Mill Run, Pennsylvania, USA, Fallingwater incorporates large boulders into interior living spaces and is oriented with the geometry of a landscape created by the interplay of mountain and climate. Built to showcase local sandstone, Fallingwater is of the terrain. Building stone was quarried near the house from a 2-m-thick zone of quartzose medium to thin-bedded, fine- to very fine-grained sandstones in the Pennsylvanian upper Pottsville Formation. The building stone has abundant trace fossils and ripple marks, and is interpreted to have been deposited in shoreface environments with some tidal influence, or possibly in tidal flat environments. The house rests on sandstone bedrock of the Homewood sandstone, a Middle Pennsylvanian unit within the upper Pottsville Formation. At Fallingwater, the Homewood sandstone is interpreted to fill an incised valley with coarse, fluvial sandstones common in the lower part of the valley fill and finer-grained fluvial sandstones with possible evidence of marine or brackish influence in the upper fill. The Fallingwater building stone unit overlies the Homewood sandstone, above an interpreted marine flooding surface. Thickening of the Homewood sandstone in synclines suggests that deposition was influenced by Alleghanian deformation. Natural fractures in competent bedrock controlled the orientation of Bear Run at Fallingwater, and the fit of the house within the three-dimensional landscape of the valley, stream, and waterfall. Variation in natural fractures in bedded versus massive sandstone layers appears to have controlled the azimuths of the edges of the waterfalls at Fallingwater. Creation of the Fallingwater sandstone member of the Pottsville Formation is proposed.

Abstract The Allegheny Portage Railroad, just one leg of the Pennsylvania Mainline Canal system, was the first railroad over the Allegheny Mountains, an imposing physiographic barrier to westward migration in the early 1800s. Construction of the canal system began in 1826 and continued until ca. 1840 without interruption. The Allegheny Portage Railroad began construction in 1831 and opened for business in 1834. This astonishing engineering feat took less than four years for completion, despite the necessity of 10 inclined planes and the use of the new-fangled railroad locomotives. Construction made use of many of the natural resources occurring along and adjacent to the right-of-way, especially the Pennsylvanian-aged sandstones used for the “sleepers” that held the rails in place. Travel occurred in sectional canal boats, boats that were built in two or three pieces that could be easily loaded onto rail cars. Passengers and goods were loaded onto the boat sections in Philadelphia, which were then hauled by horse or locomotive to the Susquehanna River west of Lancaster. The boats traveled north on the Susquehanna River canal to the mouth of the Juniata River north of Harrisburg, then along the Juniata River canal to Hollidaysburg near the foot of Allegheny Mountain. There, the boats were taken from the water, loaded onto rail cars, and hauled over the mountain on the Allegheny Portage Railroad to Johnstown where they were unloaded into the Conemaugh River canal for the journey to Pittsburgh. A New Allegheny Portage Railroad was built in the 1850s to bypass the inclined planes. It was no sooner built, however, when the state sold the entire canal system to the Pennsylvania Railroad for less than half the cost of construction. The Pennsylvania Railroad promptly dismantled the Allegheny Portage Railroad and filled in the canals. Today, the Allegheny Portage Railroad National Historic Site oversees and administers the preservation of the few remaining aspects of the old railroad.

Abstract The Allegheny Portage Railroad, just one leg of the Pennsylvania Mainline Canal system, was the first railroad over the Allegheny Mountains, an imposing physiographic barrier to westward migration in the early 1800s. Construction of the canal system began in 1826 and continued until ca. 1840 without interruption. The Allegheny Portage Railroad began construction in 1831 and opened for business in 1834. This astonishing engineering feat took less than four years for completion, despite the necessity of 10 inclined planes and the use of the new-fangled railroad locomotives. Construction made use of many of the natural resources occurring along and adjacent to the right-of-way, especially the Pennsylvanian-aged sandstones used for the “sleepers” that held the rails in place. Travel occurred in sectional canal boats, boats that were built in two or three pieces that could be easily loaded onto rail cars. Passengers and goods were loaded onto the boat sections in Philadelphia, which were then hauled by horse or locomotive to the Susquehanna River west of Lancaster. The boats traveled north on the Susquehanna River canal to the mouth of the Juniata River north of Harrisburg, then along the Juniata River canal to Hollidaysburg near the foot of Allegheny Mountain. There, the boats were taken from the water, loaded onto rail cars, and hauled over the mountain on the Allegheny Portage Railroad to Johnstown where they were unloaded into the Conemaugh River canal for the journey to Pittsburgh. A New Allegheny Portage Railroad was built in the 1850s to bypass the inclined planes. It was no sooner built, however, when the state sold the entire canal system to the Pennsylvania Railroad for less than half the cost of construction. The Pennsylvania Railroad promptly dismantled the Allegheny Portage Railroad and filled in the canals. Today, the Allegheny Portage Railroad National Historic Site oversees and administers the preservation of the few remaining aspects of the old railroad.

Abstract The latest Devonian (Famennian) is characterized by an extensive Southern Hemisphere glaciation. Deposits resulting from this glaciation are present in several formations in the mid-Atlantic region, including the Hampshire, Catskill, Rockwell, and Spechty Kopf. The Hampshire (= Catskill) Formation exhibits a noticeable stratigraphic change upsection from the middle to the top. The middle part consists of thick intervals of red, channel-phase sandstones with thin overbank siltstone and mudstone. These mudstones contain poorly developed, calcareous paleosols. The top of the Hampshire Formation consists of greenish-gray sandstones containing abundant coaly plant fragments, coalified logs, and pyrite, interbedded with thick paleo-Vertisols. The upsection increase in preserved terrestrial organic matter suggests the onset of environmental conditions that became increasingly wet. The Late Devonian escalation in climate wetness culminated in the development of a stratigraphically and spatially restricted succession of diamictite-mudstone-sandstone interpreted as having formed in glacial and proglacial environments. These glacial environments are recorded in the lower Rockwell Formation of western Maryland and contemporaneously deposited intervals of the Spechty Kopf Formation of northeastern Pennsylvania. Sheared and massive diamictite facies are interpreted as lodgement and meltout deposits, respectively; whereas, bedded diamictites are interpreted as resedimented deposits. The diamictite facies is locally overlain by a mudstone facies with variable characteristics. Both the massive and deformed mudstone lithofacies are interpreted as a clast-poor, subaqueous glaciolacustrine deposit. Laminated mudstones are interpreted as forming in quiet glaciolacustrine environments. The pebbly sandstone facies is interpreted as proglacial braided outwash deposits that both preceded glacial advance and followed glacial retreat.