| rock unit | Characteristics |
| Navarro Group | Thick section of claystone--Blackland Prairie substrate |
| Taylor Group | Calcareous claystone and marl--Blackland Prairie substrate |
| Austin Group | Chalk and marl with local pyroclastic material |
| Eagle Ford Formation | Shale; local siltstones |
| Buda Formation | Limestone; not an aquifer |
| Del Rio Clay | Claystone and shale--forms seal above Edwards aquifer |
| Georgetown Formation | Nodular limestone--upper part of Edwards aquifer |
| Edwards Group | Limestone--karstified host rocks for Edwards aquifer |
| Comanche Peak Formation | Marly limestone |
| Walnut Formation | Hard and soft limestone |
| Glen Rose Formation | Alternating beds of limestone, dolomite, and marl--numerous small, perched aquifers |
| Hensel Sand | Sandstone and conglomerates--upper member of "Trinity Sand aquifer" |
| Cow Creek Limestone | Limestone--locally water-bearing |
| Hammett Shale | Shale and claystone with sandstone lenses |
| Sycamore Sand | Sandstone and conglomerates--basal Cretaceous rock unit in Central Texas |