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.

Benthic samples were collected on a 1-mi grid from Copano Bay, Texas, in March and April, 1976. Seventy-four molluscan species, including 33 pelecypods, 40 gastropods, and 1 scaphopod were taken from 93 stations in Copano Bay.