Named for exposure in bluffs along Rio Grande in Val Verde Co, TX (southeastern Permian basin). Exposed from a point 2 1/2 mi south of Del Rio, TX down the Rio Grande to Sycamore creek, forming a bluff 25-75 ft high, with a dip apparently not less than 100 ft/mi. Overlies Vola limestone [Buda Limestone]. Overlain by Pinto limestone (new) [Austin Chalk]. Lime flags are grayish-white in color, laminated to flaggy in structure, and separated into bands by laminated clays. At Sacatosa creek, lower strata contain considerable bituminous matter and the remains of fishes; higher beds are also sufficiently bituminous to yield fetid odor when struck with a hammer. An undescribed species of INOCERAMUS is the principal fossil; a few small ammonites observed near top. Flags are uniform in structure from base to top, the principal variation being in thickness; in places they are shaly, but are commonly flags of various thicknesses, frequently showing on a transverse surface alternate parallel laminae of white and yellow; weathered surfaces are from light yellow to reddish, and in some places beds of deeper yellow or even orange hue are found; thickness based on apparent dip is 600 ft. Correlated with Eagle Ford shales of the Colorado River section. [Mapped as Eagle Ford Group by Bureau of Economic Geology (Barnes, 1977). Age is Late Cretaceous.]

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