The Geologic Atlas of Texas gives a colorful view of the geologic formations throughout the state. In addition to print copies of the maps, which are available for 4-hour check out at the Checkout Desk on the 3rd floor, the GAT can be viewed online.
The University of Texas at Austin has an exceptional collection of maps, many in digital form at the Perry Castaneda Library.
A 19th-century "Bird's Eye View of San Marcos" is available from the Texas General Land Office. Just enter "89205" in the Map/Document # search box to see what has changed and what remains the same.