The Carrizo Sand (Eocene), the basal unit of the Claiborne Group, can be recognized in the subsurface throughout much of southeastern Arkansas and is correlated with the Carrizo Sand of Louisiana and the Meridian Sand Member of the Tallahatta Formation of Mississippi. The term Carrizo Sand is appropriate for use in Arkansas, as the stratigraphic terminology most workers apply to the Claiborne Group in Arkansas conforms with the terminology of Louisiana. A surface exposure of the Carrizo Sand in Arkansas is lithologically identical with described exposures of the Carrizo in northwestern Louisiana.