First used in discussion of Upper Cretaceous volcanics in vicinity of Pilot Knob, a hill 6-8 mi south-southeast of the State Capitol, Austin, Travis Co, TX in Ouachita tectonic belt province. Also called St. Edwards ash. Consists of igneous material, extruded in the form of ash and cinders, that locally accumulated to considerable thickness. A section near Williamson Creek (pl. 16, section 3) contains the Pilot Knob tuff (new) within Dessau formation (new) and a similar but younger bed (within the basal Burditt formation) derived from the St. Edwards eruption (St. Edwards tuff). Type locality not designated; derivation of name not given [probably named from St. Edwards University]. [Is considered to be an informal unit.] Age is Late Cretaceous.

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