Assigned to the newly named Nacimiento group as the lower formation near Cuba, Sandoval Co, NM in the San Juan basin. Not identified outside northwest NM. Unconformably overlies Lewis shale or Laramie formation. Unconformably? underlies Torrejon formation, upper formation of Nacimiento group. Two sections measured. The first is along the Puerco River south and east of Nacimiento (called Cuba by the PO) where the Puerco is 558 ft thick and consists of gray, tan, variegated shale interbedded with yellowish, brown, tan, gray sandstone. The shale has coal streaks. The sandstone may be massive, coarse grained, lenticular. Sandstone makes up 320 ft of the 558 ft thick section. The second is on the east fork of Arroyo Torrejon, four miles east of Farmington road where the Puerco is 210 ft thick and consists of gray, red, purple drab shale and tan sandstone. The shale may be sandy. The sandstone may be massive, coarse grained. Sandstone makes up 80 ft of the 210 ft thick section. Not easily separated from the overlying Torrejon except for "fossil evidence." Fossils: mammals, mullituberculates, creodonts, insectivores, taeniodonts, condylarths, amblypods, reptiles, birds, mollusks, flora; fossils listed; a Mesozoic fauna extinct in the Eocene. Shallow lake and lagoon deposit.

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

Neither Puerco nor Torrejon recognized as formations in this report. One unit name, the Paleocene Nacimiento Formation, applied to rocks above the Ojo Alamo Sandstone (restricted). A Puerco and Torrejon fauna shown as present in Nacimiento.

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