Pg. 263; see also 1953, Smithsonian Misc. Colln., v. 121, no. 1, p. 18-20, 24 (fig. 9), 30 (table 2). San Jon formation. Consists chiefly of dark-blue-gray clay grading laterally into greenish clay and into reddish compact sandy alluvium towards borders of basin. Thickness 0 to 50 feet. Disconformably underlies Sand Canyon formation (new). Rests on nearly horizontal but slightly irregular top of unit referred to as basal sand that unconformably overlies Purgatoire formation. Bones of extinct bison and artifacts found in top of blue clay. Age is late Pleistocene.
Type exposure: San Jon site, approximately 10 mi south of San Jon, Quay Co., eastern NM.

Source: US geologic names lexicon (USGS Bull. 1200, p. 3446).