The eastern part of Williamson County is in the black land belt of Texas where roads must be surfaced to be passable in wet weather. Road materials are scarce in this area, so much of the time spent on the mineral resource survey was concentrated on finding gravel.

In east-central Texas, or the area between the Colorado
and Trinity Rivers, the Wilcox Group (lower Eocene) is divided
into three formations. Up section they are the Hooper,
Simsboro, and Calvert Bluff. At Alcoa and Butler, lower Calvert