Studies of physiographic relations and of fossil molluscan faunas made in the Pecos River valley region (Val Verde County to the Texas�New Mexico border) reveal extensive, well-pedimented surfaces southwest of the river extending from the Davis Mountains to near the present channel.
The Blach Ranch and Breckenridge limestone members of the Thrifty formation are the most persistent mappable rock units in the Cisco group of the Brazos and Trinity River valleys. These limestone beds occur above the complex post-Bunger deposits of the Graham formation and below an equally complex section of Harpersville rocks.
Forty-three species belonging to 28 genera, 12 species of brachipods belonging to 8 genera, and 1 species of gastropods are described from the Morgan Creek, Point Peak, and San Saba Members of the Wilberns Formation in the Llano Uplift. Systematic descriptions include 1 new trilobite genus, 6 other new trilobite species, 1 new brachipod genus, 2 new brachiopod species, and one new brachiopod subspecies.
