Consists of thick bed of glauconitic sandstone which forms persistent marker horizon. Is the top member of Cap Mountain formation. Underlies Wilberns formation; overlies Hickory sandstone. Age is Late Cambrian. Report includes correlation chart.
Type locality not designated. Probably on southwest side of Lion Mountain along State Highway 29. Named from Lion Mountain in northwest part of Burnet quadrangle, Burnet Co., central TX, on Llano uplift.

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

In central TX, Llano uplift, the Lion Mountain sandstone member--formerly part of Cap Mountain formation--reassigned as top member of Riley formation (new). Overlies Cap Mountain formation and underlies Wilberns formation. Thickness is 24 ft. Consists of highly glauconitic sandstone which contains limestone lenses in lower part. Topographically it forms a bench recognizable in aerial photographs. Age is Late Cambrian.

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

Riley formation in the study area (Llano uplift of central TX) ranges from about 600 to nearly 800 ft thick; it is thickest in southeast Llano Co. and thinnest in northwest corner of uplift; it overlies pre-Cambrian rocks; it underlies Wilberns formation; it is assigned a Late Cambrian age. Cross sections. Riley is divisible into the Hickory sandstone member, at base, Cap Mountain limestone member, in middle, and Lion Mountain sandstone member, at top. Upper boundary of Hickory modified; contact with overlying Cap Mountain placed at top of a noncalcareous sandstone beneath a zone of alternating impure dark brown limestone and calcareous sandstone; this contact is also a distinct topographic and vegetational break. The Hickory-Cap Mountain contact was previously placed at an indefinite point or thin the sequence. The upper contact of the Lion Mountain is revised in that Lion Mountain underlies the newly named Welge sandstone member of the Wilberns.

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

In central TX, Llano uplift, faunal studies show hiatus between Lion Mountain sandstone member and overlying Wilberns formation. Contact is either a sharp lithofacies change that is older in the west than to the east, or a disconformity whose faunal hiatus decreases in magnitude in southeastern direction. Age is Late Cambrian.

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

In central TX, Llano uplift, revised as top member of Riley Formation of Moore Hollow Group (new). Moore Hollow Group includes Riley Formation below and Wilberns Formation above, and ranges in age from Middle Cambrian to Early Ordovician. Unconformably underlies Wilberns Formation with sharp boundary and overlies Cap Mountain Limestone Member with ill-defined boundary. Thickness is 49 ft at type section. Thins to southeast. Isopach map. Correlation chart. Geologic maps. Age is Late Cambrian, Dresbachian.

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