Formerly called "persistent horizon marker" by J. H. Gardner (Gardner, 1910). Here named as bed at base of early Paleocene Ojo Encino Member (new) of early and late Paleocene Nacimiento Formation (revised). Named for local spring called Penistaja at sec 14, T20N, R4W near type where there are excellent exposures. Type section at West Flank Torreon Wash, offset from NE1/4 NW1/4 NW1/4 sec 27, T21N, R5W to SE1/4 SE1/4 SW1/4 sec 28, T21N, R5W, Deer Mesa 7.5 min-quad, south of Kutz Canyon in southern San Juan basin, Sandoval Co, northwestern NM. Dip of strata <5 deg. See also the Nacimiento's composite section and well log correlation (Figs. 5, 9, and 10). Extends to Mesa de Cuba (Sandoval Co), and to Chico Springs and De-Na-Zin Wash (San Juan Co), northwestern NM. Outcrops as extremely prominent ledges and cuestas. At type consists of resistant grayish orange, fine-grained, planar to trough cross-bedded sandstone complex with silicified wood and cannonball concretions. Described at Mesa de Cuba as grayish orange to yellowish gray; very fine grained; well sorted subrounded; subarkosic; very calcareous; with pale brown cannonball concretions; sandstone is multistoried with numerous channels showing basal scours and containing epsilon crossbeds with clay drapes; soft sediment deformation. At type, total thickness is 6.5 m; elsewhere in basin, ranges to as much as 60 m. Base of the Penistaja is a sharp, scoured contact (probably a disconformity) into the underlying mudstone of early Paleocene Arroyo Chijuillita Member (new). Overlain by the colorfully banded Ojo Encino (new). Correlation determined by subsurface electric-log signatures in wells and by surface measured sections. Age is early Paleocene (late Danian) based on classic Torrejonian mammal faunas and magnetostratigraphy. Report includes geologic sketch map, correlation charts, field notes, composite sections, well logs, and measured sections.

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