This Guidebook represents an updating of Bureau of Economic Geology Guidebook No. 5, Field Excursion-Geology of Llano Region and Austin Area. It also represents a modification of Geology of the Llano Region and Austin Area, Texas, published by the Shreveport Geological Society in 1971.

Basic geologic, hydrologic and engineering criteria on which selection of sanitary landfill sites should be based include (1) thickness, excavation characteristics, permeability, solution-holding capacity, and reactivity of host and cover materials; (2) hydrologic properties including depth to water table, season variation in position of water t

Regional surface and subsurface studies indicate that thick deltaic (Queen City Formation) and thin shelf (Reklaw and Weches Formations) sequences compose the stratigraphic interval between the top of the Carrizo Sand and the base of the Sparta Formation.

The Eastern Shelf was a constructional platform developed on the margin of the sediment-starved Midland Basin during Late Pennsylvanian and Early Permian time. A mixed terrigenous-carbonate sedimentary province characterized the shelf during most of its history. Sediments were derived from highlands to the east and northeast.

Mountain-bounded basins or bolsons are the most important aquifer systems throughout most of southwestern and western United States and northern Mexico. The dissection of the Presidio Bolson by the Rio Grande and its tributaries has afforded an ideal situation for detailed study of the stratigraphy of one of these important aquifer systems.