At the northern end of the Coahuila platform, the thinned Comanchean sequence consists of the newly named Sixshooter group of carbonate formations underlain by the newly named Yearwood formation.

The first entry in the Guidebook Series details a field excursion to the Eastern Llano Region of Central Texas in 1958. Retrace the footsteps of Virgil Barnes and the other state geologists in attendance: 

Stop 1. Honeycut Bend

Pleistocene-age fossil horses of Texas belong to at least three faunal assemblages. The oldest contains Hippotigris (= Plesippus) which disappeared before Yarmouthian time.

The eastern margin of the High Plains in central western Texas affords particularly good opportunity for study of late Cenozoic geology.