Named as a member of San Jose Formation for exposures near mouth of Canoncito de las Yeguas about 1 1/4 mi northwest of Llaves P.O., Rio Arriba Co, NM in San Juan basin. The type section is a measured composite of N1/2 sec 18, T25N, R1E for the lower part and of SW1/4 sec 4, T25N, R1W for the upper part. The lower part is 695+ ft thick and the upper part is 450 ft thick at the type. Present in northern part of area. Composed mostly of massive beds of resistant arkosic conglomeratic sandstone. Some thin red and variegated shale and shaly sandstone beds. Sand is mainly quartz or quartzite grains that are angular to subangular. Some fragments of pink to gray feldspar. The pebbles and cobbles are rounded, mostly metaquartzite, but some are granite, gneiss, and schist. Overlies Cuba Mesa Member (new) of San Jose. Intertongues with Regina Member (new) and with an unnamed member of San Jose. Underlies and intertongues with Tapicitos Member (new) of San Jose. Of early Eocene age. Geologic map. Correlation chart. Cross sections. Measured sections.

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