This field trip is a follow-up and complement to the publication of the Hydrogeologic Atlas of the Hill Country Trinity Aquifer, Blanco, Hays, and Travis Counties, Central Texas (referenced as Wierman et al., 2010 or “HA” throughout this guidebook). For reference, the HA is included as an Appendix at the end of this guidebook. The HA and work presented in this guidebook builds upon the analyses done by many geoscientists—too many to name here, but many are included in the references of the HA.