|Name||Jackson Group, undivided|
|Geologic age||Oligocene and Eocene|
Unconsolidated > Fine-detrital > Clay (Bed)
Sedimentary > Clastic > Sandstone (Bed)
Sedimentary > Clastic > Siltstone (Bed)
|Comments||clay, sandstone, siltstone, and tuff. as much as 875 ft thick, mapped generally south of Frio River|
Bureau of Economic Geology, 1974, Seguin Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1966, Texarkana Sheet, Geologic Atlas of Texas, University of Texas, Bureau of Economic Geology, scale 1:250,000.
Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.
|Counties||Duval - Jim Hogg - La Salle - McMullen - Starr - Webb - Zapata|