[Name proposed for the] chalky limestone exposed in bluffs along Rio Grande in vicinity of Piedro Pinto Creek, Kinney County, TX [Ouachita tectonic belt province] and continuing downstream to Las Moras Creek, Maverick County, TX [Gulf Coast basin]. Overlies Val Verde flags (new). Underlies Upson clays (new) of Eagle Pass division (revised). Consists of chalky limestone throughout; beds become somewhat more massive but broken toward the top. Limestone beds are separated by limy shales at the base, then by calcareous clays, then by purer clays, and finally by calcareous clays again. Fossils include INOCERAMUS, GRYPHAEA, AMMONITES, BACULITES, NAUTILUS, EXOGYRA PONDEROSA and E. COSTATA; occurrence of E. PONDEROSA and E. COSTATA so low in the section is worthy of note. Sections described at Cow Creek, Texaquito Creek, and Las Moras Creek. Thickness, based on apparent dip, is 1,500 feet. Is same as Austin limestone of the Colorado River section. [Mapped as Austin Chalk by Bureau of Economic Geology (Barnes, 1977). Age is Late Cretaceous.]
[GNC records (US geologic names lexicons, USGS Bull. 896 (p. 1667) and 1200 (p. 3040)) state "named from Pinto Creek, Val Verde Co., TX." GNU records (USGS DDS-6; Denver GNULEX) state "type not designated; derivation of name not stated, apparently [named] from Piedro Pinto Creek, in Kinney Co., TX." GNC records (US geologic names lexicons, USGS Bull. 896, 1200) indicate this publication is the original reference. GNU records (USGS DDS-6; Denver GNULEX) do not. Here, it is classified as the original reference.]

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