Named for Pillar Bluff on Pillar Bluff Creek, 5 mi southwest of Lampasas, south of Lampasas Co. line in Burnet Co., TX on the Llano uplift; this locality is the type locality. These rocks were formerly thought to be part of the Lower Mississippian Chappel formation. Geologic map; shown as single line in 3+ small areas 100 +/-ft long just north of Pillar Bluff. [Not a unit of formation rank; not mappable at a conventional scale.] Thickness not estimable partly due to the type of preservation in openings in the Ellenburger floor of the Helderberg sea. Consists of two types of limestone. One is fine- to coarse-grained, gray to ivory, crowded with fossils, easily broken. The second is fine to very fine grained, gray to olive-drab, slightly dolomitic, few macrofossils, resistant to fracture, glauconite grains. Fauna (brachiopods, conodonts) listed. Formation distinguished by fauna of Helderberg (Early Devonian) age. Is younger than the Ordovician Ellenburger group and older than Mississippian Chappel formation.

Source: GNU records (USGS DDS-6; Denver GNULEX).