Prepared in conjunction with the GSA Southeastern and Northeastern Sections Joint Meeting in Reston, Virginia, the four field trips in this guide explore various locations in Virginia, Maryland, and West Virginia. The physiographic provinces include the Piedmont, the Blue Ridge, the Valley and Ridge, and the Allegheny Plateau of the Appalachian Basin. The sites exhibit a wide range of igneous, metamorphic, and sedimentary rocks, as well as rocks with a wide range of geologic ages from the Mesoproterozoic to the Paleozoic. One of the trips is to a well-known cave system in West Virginia. We hope that this guidebook provides new motivation for geologists to examine rocks in situ and to discuss ideas with colleagues in the field.

Abstract During the Pleistocene, the Laurentian Ice Sheet extended southward into western Pennsylvania. This field trip identifies a number of periglacial features from the Pittsburgh Low Plateau section to the Allegheny Mountain section of the Appalachian Plateaus Province that formed near the Pleistocene ice sheet front. Evidence of Pleistocene periglacial climate in this area includes glacial lake deposits in the Monongahela River valley near Morgantown, West Virginia, and Sphagnum peat bogs, rock cities, and patterned ground in plateau areas surrounding the Upper Youghiogheny River basin in Garrett County, Maryland, and the Laurel Highlands of Somerset County, Pennsylvania. In the high lying basins of the Allegheny Mountains, Pleistocene peat bogs still harbor species characteristic of more northerly latitudes due to local frost pocket conditions.

Abstract The stratified red beds of the Catskill Formation are conspicuous in road cut exposures on the Allegheny Plateau of north-central Pennsylvania. During this field trip we will visit and explore several fossil localities within the Catskill Formation. These sites have been central to recent investigations into the nature of Late Devonian continental ecosystems. By the Late Devonian, forests were widespread within seasonally well-watered depositional basins and the spread of plants on land from the late Silurian through the Devonian set the stage for the radiation of animals in both freshwater and terrestrial settings. A diverse assemblage of flora and fauna has been recovered from the Catskill Formation including progymnosperms, lycopsids, spermatophytes, zygopterid and stauripterid ferns, barinophytes, invertebrates and invertebrate traces, and vertebrates such as placoderms, acanthodians, chondrichthyans, actinopterygians, and a variety of sarcopterygians including early tetrapods. Since the early 1990s, highway construction projects along the Route 15 (Interstate 99) have provided a new opportunity for exploration of the Catskill Formation in Lycoming and Tioga counties. The faunas along Route 15 are dominated by Bothriolepis sp. and Holoptychius sp. and also include Sauripterus taylori and an assortment of other interesting records. The most productive Catskill site, and the source of early tetrapod remains, is Red Hill in Clinton County. Red Hill presents a diverse and unique flora and fauna that is distinct from Route 15 sites, and also provides a spectacular section of the alluvial plain deposits of the Duncannon Member of the Catskill Formation.

Early flow paths can be traced along structural segments (single fractures, fracture intercepts, or zones of closely spaced fractures) through hundreds of kilometers of branchwork caves in structurally complex settings along the eastern Allegheny Plateau of West Virginia, USA. Identification of the early fracture conduits presupposes the following primary conditions: (1) prominent fracture traces are retained on bedrock perimeters; (2) fracturing associated with later cave enlargement is minimal and distinguishable from transmissive fractures; (3) conduit enlargement and modification are not so extensive or so directed as to have totally destroyed the fractures; and (4) there is minimal covering of relevant fracture traces by clastic or chemical sedimentation. Criteria used to infer structural segments include: (1) the presence of anastomoses or other dissolutional features along fractures; (2) the presence of tubes, half tubes, or segments of passage concordant to fractures; (3) the existence of anastomoses and other tubes that grow upward from initially transmissive fractures; (4) the presence of features of entrenchment that are lower than remnant tubes, half tubes, and most early parts of joint fissures; and (5) the continuity of flow along fractures, except at locations of dissolutional mining to create mined segments. If structural segments are identified and mapped with high-precision leveling surveys, a framework can be provided to decipher many details of flow-path integration and enlargement. It is then possible to reconstruct cave history using evidence provided by analysis of passage morphology, sediments, and the relationships of cave features to local and regional surface features.

The Blue Ridge and Great Valley of western Virginia are part of a detached master thrust sheet that extends through the central-southern Appalachian change of trend and has a root zone situated east of the Blue Ridge under the Piedmont. The mapped Pulaski fault and North Mountain fault crop out in the Great Valley as splay faults terminating in thrust tip anticlines and merge at depth with the buried master detachment floored primarily in Upper Ordovician Martinsburg Shales. Overall transposition of the thrust sheet from the root zone indicates that as much as 32 km (20 mi) of displacement may be translated westward into the Valley and Ridge proper and Allegheny Plateau as initial cover shortening above the Martinsburg Shale. Within the Great Valley and into the Roanoke recess at the juncture of the central and southern Appalachians, much of the cover shortening of this master sheet is accommodated by the Pulaski and North Mountain faults. From northeast to southwest, movement on the outcropping and buried master segment of the North Mountain fault decreases, and the surface fault terminates in southern Rockbridge County. Displacement on the Pulaski fault increases from northeast to southwest, and we infer that it assumes the decreasing displacement on the outcropping and buried segments of the North Mountain fault by displacement transfer.