ABSTRACT Multiport monitor wells have been used by the Barton Springs/Edwards Aquifer Conservation District (BSEACD) to study complex, multilayer, and stacked aquifers in central Texas. Much of the data from water wells that are used for hydrogeological studies are of limited use owing to the thickness of the aquifers, vertical variation in hydraulic properties, and the often-uncertain completion of the wells. To address these concerns, hydrogeologists and engineers have employed various methods, such as installation of nested wells, multilevel completions in a single borehole, and multiport wells. The BSEACD has used multiport wells to determine vertical variations in an aquifer and the hydraulic relationships between stacked aquifers. With multiport wells, properties such as hydraulic head, temperature, hydraulic conductivity, and water quality of discrete units within an aquifer can be determined. The use of multiport wells has shown how portions of the Upper Trinity lithologic units are hydraulically connected to the overlying Edwards lithologic units, and how the Edwards Aquifer is hydraulically isolated from the Middle and Lower Trinity Aquifers.

ABSTRACT The Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer is a prolific karst aquifer system containing the fourth largest spring in Texas, Barton Springs. The Barton Springs segment of the Edwards Aquifer supplies drinking water for ~60,000 people, provides habitat for federally listed endangered salamanders, and sustains the iconic recreational Barton Springs pool. The aquifer is composed of Lower Cretaceous carbonate strata with porosity and permeability controlled by depositional facies, diagenesis, structure, and karstification creating a triple permeability system (matrix, fractures, and conduits). Groundwater flow is rapid within an integrated network of conduits discharging at the springs. Upgradient watersheds provide runoff to the recharge zone, and the majority of recharge occurs in the streams crossing the recharge zone. The remainder is direct recharge from precipitation and other minor sources (inflows from Trinity Group aquifers, the San Antonio segment, the bad-water zone, and anthropogenic sources). The long-term estimated mean water budget is 68 ft 3 /s (1.93 m 3 /s). The Barton Springs/Edwards Aquifer Conservation District developed rules to preserve groundwater supplies and maximize spring flow rates by preserving at least 6.5 ft 3 /s (0.18 m 3 /s) of spring flow during extreme drought. A paradox of the Barton Springs segment of the Edwards Aquifer is that rapid recharge allows the Barton Springs segment of the aquifer to be sustainable long term, but the aquifer is vulnerable and limited in droughts. The karstic nature of the aquifer makes the Barton Springs segment vulnerable to a variety of natural and anthropogenic contaminants. Future challenges will include maintaining the sustainability of the aquifer, considering climate change, population growth, and related land-use changes.

ABSTRACT Outcrops of Late Cretaceous Gulf Series strata (Woodbine, Eagle Ford, and Austin) in the Dallas area expose middle Cenomanian to the early Campanian (96 to ˜ 83 Ma) rocks, which are well known in the subsurface of the oil-rich East Texas Basin. Together with the underlying Comanche Series and overlying younger Gulf Series, this set of strata provides a record of the last 50 million years of the Cretaceous. Although both marine and terrestrial vertebrates are known in this interval, the Late Cretaceous record is primarily marine. On this field trip, sites are visited that have yielded sharks, bony fish, turtles, dinosaurs, crocodiles, pterosaurs, mammals, long- and short-necked plesiosaurs, and a classic record of mosasaur evolution.

ABSTRACT The purpose of this trip is to visit an internationally famous Quaternary vertebrate paleontology site, Friesenhahn Cave, on the eastern margin of the Edwards Plateau in the heart of the central Texas Hill Country. This site has a very long history of scientific investigations beginning in the early twentieth century and continuing today. The cave has produced the fossil remains of more than 50 vertebrate taxa, including amphibians, reptiles and mammals. However, the abundant remains of an extinct scimitar cat, Homotherium serum, including juvenile individuals along with hundreds of teeth, cranial, and postcranial elements of juvenile mammoths, Mammuthus cf. M. columbi, make it an especially unique site. Our visit to Friesenhahn Cave will focus on its physical setting, cave sediment stratigraphy, potential age and taphonomy as they relate to the adaptations of Homotherium in the late Pleistocene of central Texas and its relationship to its potential prey, juvenile mammoths. We will also discuss recent studies of the cave itself, and its protection for future investigations by Concordia College.

ABSTRACT This trip follows part of the route taken by E.T. Dumble, R.A.F. Penrose, Jr. (later president of and great benefactor to the Geological Society of America), and R.T. Hill as they surveyed the geology from the vantage point of the Colorado River between Austin and La Grange during the Geological Survey of the State of Texas in April of 1889. This year has particular significance because it is the same year that Penrose joined the Geological Society of America. The river has changed in flow regime, and many outcrops have weathered or been flooded. This trip passes through the primarily Claiborne (middle Eocene) geologic section between Bastrop and Smithville, Texas, and illustrates the difficulties to be faced when retracing historic geological surveys. The group will be using and testing a mobile application developed specifically for this field trip theme.

ABSTRACT This field trip examines exposures of transgressive and highstand marine deposits of the Sabinetown transgression that forms the upper part of the Calvert Bluff Formation of the Wilcox Group in the outcrop belt. The horizon of maximum flood in the Sabinetown transgression at Bastrop contains molluscs and diverse vertebrate fossils characteristic of open marine environments. The highstand deposits coarsen upward and are capped with a well-developed paleosol. These deposits are dated as early Eocene.

Abstract This volume, prepared in conjunction with the 47th Annual Meeting of the GSA South-Central Section, contains four guides that focus on sedimentology and paleontology in Texas. A theme of exploration threads its way through the trips, all of which can trace their roots to the work of early geologic explorers. One trip retraces part of the 1889 Dumble survey that explored the geology along the Colorado River between Austin and La Grange, Texas, while another takes readers to an internationally famous Quaternary vertebrate paleontology site, studied since the beginning of the twentieth century, inside Friesenhahn Cave in the central Texas Hill Country. Another guide visits Paleocene- to Eocene-age sediments derived from the Rocky Mountains and transported via rivers to the Houston Embayment, building out the continental shelf, while a fourth explores Late Cretaceous Gulf Series strata in the Dallas area.