Although isolated pseudo-karst caves occur throughout Texas, only those areas with several caves of similar origin are presented. Dolomite dissolves slower than limestone, but is very similar. The BFZ is narrow and runs south from Dallas to San Antonio, then turns west and nearly reaches Del Rio. It contains thick-bedded to massive Cretaceous limestone and some dolomite beds from the Edwards Group, Glen Rose, Buda, Georgetown, Austin, and Anacacho formations. Abundant faults, all related to Miocene-age structural activity, are generally downthrown toward the Gulf of Mexico.
Joints are more numerous and determine the orientation of most caves.
For the most part, cave fill is either old, pre-entrance red clay and kaolinite, or modern black soils eroded from the surface probably because of overgrazing. The BFZ is closely related to but separated from the Edwards Plateau by a strip where the Edwards Group limestones have been erosionally removed. It is one of the largest continuous karst areas in the United States. Many of the caves, some quite extensive, are confined to small vertical intervals, either by lithology of the confining beds or by still-stands of nearby rivers. Vertical caves are less common.