ABSTRACT The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer is a shallow unconfined aquifer that supports several historical springs, perennial streamflow to Lake Waco, and water for rural households and livestock. Secondary porosity in the aquifer is from neotectonic fractures and epikarst in the Georgetown and Edwards Formations. The fractures produce an “effective” porosity of ~1%. Thin soils allow rapid recharge, as indicated by water-level responses in wells within 24 h of rainfall events. Discharge is generally along second-order streams; topography is the dominant influence on groundwater flow direction. The interbedded clays in the Georgetown Formation create a preferred horizontal to vertical anisotropy. The fractured nature of the aquifer produces local heterogeneity, but regionally, the aquifer acts as a diffuse rather than conduit flow system. Weathering results in a layered flow system with greater effective porosity and permeability in an upper zone compared to the deeper zone. Washita Prairie springs are perennial, with discharges generally <0.05 m 3 /s. The groundwater is calcium bicarbonate facies with total dissolved solids (TDS) <500 mg/L in most springs and shallow-zone wells. Water quality in deeper wells is more variable, as these encounter the deeper flow system with slower circulation and higher TDS. The shallow water table and rapid recharge through fractures allow surface activities to impact water quality, and nitrate levels appear to be elevated above average background values in places. The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer may be able to supply over 50,000,000 m 3 of sustainable water on an annual basis with continued study and proper management.

ABSTRACT The Edwards (Balcones Fault Zone) Aquifer in central Texas is typically defined as having three segments: the San Antonio, the Barton Springs, and the Northern segment, which are separated by groundwater divides or points of discharge. The San Antonio segment of the Edwards Aquifer is defined as extending from east of Brackettville in the west to Hays County in the east. The San Antonio segment has been further delineated into two pools, the San Antonio Pool and the Uvalde Pool, for water management purposes. The San Antonio Pool is the larger of the two pools and is recharged by the Dry Frio, Frio, Sabinal, Medina, Cibolo, Guadalupe, and Blanco River watersheds, in addition to direct recharge and flow from the Uvalde Pool via the Knippa Gap. To a lesser extent, interformational flow between units stratigraphically above and below the Edwards Formation limestone also occurs. The most prominent points of discharge from the San Antonio Pool are Comal, San Marcos, and Hueco Springs. San Pedro and San Antonio Springs in Bexar County discharge during periods of high stage in the aquifer. There are limited numbers of additional springs in the Frio River watershed with limited discharge. Significant water is discharged from the Medina Lake and Diversion Lake (downstream from Medina Lake dam) system via conduits and surface flow to recharge paleo-alluvial deposits (Leona Gravel) in the Medina River floodplain. This discharge had previously been assumed to recharge the Edwards Aquifer, but it continues downgradient in the Leona Gravel and is lost to the aquifer.

Abstract A regional network of five interlocking stratigraphic cross-sections compiling the published work of many geologists throughout central and southwest Texas demonstrates the true stratigraphic relationships among formations of the Lower Cretaceous Fredericksburg and lower Washita subcycles. Strongly supported by a long-established ammonite zonation, these detailed stratigraphic cross-sections show lateral relations between Edwards Group formations (Kainer, Person, Fort Terrett, Segovia, Fort Lancaster, and Devils River) of the Central Texas Platform with equivalent formations of the East Texas Basin (Walnut, Comanche Peak, Goodland, Georgetown) and the Maverick Basin of South Texas (West Nueces, McKnight, Salmon Peak). These cross-sections document the following regional stratigraphic relationships: The Burt Ranch Member (basal Segovia Formation), the Regional Dense Member (basal Person Formation), and the Kiamichi Member (basal Georgetown Formation) are stratigraphic equivalents, all three being in the Adkinsites bravoensis Ammonite Zone (lowermost Washita) The peritidal Person Formation is the shelf-interior equivalent of the pelagic-shelf Georgetown Formation, except for its uppermost member, the Main Street, which forms the thin remnant Georgetown Formation on the distal Central Texas Platform. Thus the Person Formation is properly assigned to the lower Washita subcycle, not the Fredericksburg.

Abstract Uppermost Aptian-Albian-lower Cenomanian strata of the Texas Comanchean Series represent three long-term transgressive-regressive cycles: the Trinity, Fredericksburg, and Washita groups that are composed mainly of marine limestone and shale. Each group is composed of shorter term deepening-shallowing cycles. On the Central Texas San Marcos Platform and its downdip equivalents, subsurface strata above the Trinity Group are grouped into the Edwards and Washita groups. Correlations in the 1960s were based on wireline well logs and inferred biostratigraphy that correlated the upper Edwards Group Person Formation with the lower parts of the Washita Group. This correlation crosses a widespread subaerial unconformity that separates the Washita from the underlying Fredericksburg in the northern East Texas Basin and in the Fort Stockton Basin. New biostratigraphic and sedimento-logical data show that the Person actually correlates with the upper part of the Fredericksburg in the Gulf Coast.

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.