Pg. 20. Ojo Bonito stock (informal). Quartz monzonite samples from the Infiernito caldera, Chinati Peak, Cienequita, and Cuesta Del Burro East quadrangles, Presidio County, southwestern Texas, yielded K-Ar ages from 37.5 +/-0.7 Ma to 36.5 +/-0.6 Ma (biotite). Data from T.W. Duex and C.D. Henry, 1981 (Univ. Texas-Austin Bur. Econ. Geol., Geol. Circ. 81-2, 14 p.), and C.D. Henry and J.G. Price, 1984 (Jour. Geophysical Res., v. 89, p. 8765-8786); ages recalculated using decay constants of Steiger and Jager, 1977 (Earth Planet. Sci. Letters, v. 36, p. 359-362).
[Age considered Eocene to Oligocene; Eocene-Oligocene boundary 36.6 (38-34) Ma (from Geologic Names Committee, USGS, 1983 ed. geol. time scale, with additions from N.J. Snelling, 1985, The Geol. Soc. Mem., no. 10).]

Source: Publication.