Here named as lowest member of early and late Paleocene Nacimiento Formation (revised). Named for tributary of Rio Puerto called Arroyo Chijuillita just west of Mesa de Cuba at NW1/4 NE1/4 NE1/4 sec 9, T20 and 21N, R2W, Mesa Portales 7.5-min quad, south of Kutz Canyon in southern San Juan basin, Sandoval Co, northwestern NM. See also the Nacimiento's composite section and well log correlation (Figs. 5, 9, and 10). Extends to West Flank Torreon Wash and Escavada Wash (both in Sandoval Co), as well as to West Fork Gallegos Canyon, De-Na-Zin Wash, West Flank Kimbeto Wash, and to Betonnie Tsosie Wash (all in San Juan Co), northwestern NM. Outcrop habit is slope-forming in contrast to overlying more resistant, ledge-and-cuesta-forming unit. At type consists of 36% sandstone; 27% sandy, silty mudstone or muddy sandstone; 35% mudstone; and 2% lignite or coal. Distinctively drab (gray, olive, or buff), but red and green mudstones do occur. Total thickness at type is 81.2 m; ranges to 134 m. Conformably overlies, grades into, and interfingers early Paleocene Ojo Alamo Sandstone; its base readily recognized as bottom of first mudstone or sandy mudstone bed above the Ojo Alamo. Disconformably underlies (by sharp, scoured contact) early Paleocene Penistaja Bed (new) of Ojo Encino Member (new) of the Nacimiento. Correlation determined by reading subsurface electric-log signatures in wells and by surface measured sections. Age is early Paleocene (early Danian) based on Puercan and Torrejonian mammal faunas, absence of dinosaurs, and on 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).