Yegua Formation
(Middle Eocene) at surface, covers 17 % of this area Yegua Formation
Laredo Formation
(Middle Eocene) at surface, covers 17 % of this area Laredo Formation
El Pico Clay
(Eocene) at surface, covers 16 % of this area El Pico Clay
Alluvium
(Holocene) at surface, covers 5 % of this area Alluvium
Terrace deposits
(Pleistocene and Holocene) at surface, covers 4 % of this area Terrace deposits
Uvalde Gravel
(Pliocene to Pleistocene) at surface, covers 3 % of this area Uvalde Gravel
Frio Clay
(Oligocene) at surface, covers 1 % of this area Frio Clay
Carizzo Sand
(Eocene) at surface, covers 0.4 % of this area Carizzo Sand
Indio Formation
(Paleocene to Eocene) at surface, covers 0.3 % of this area Indio Formation