Augustus K. Armstrong; Reply [to discussion by Elmer H. Baltz (1969) of 'Interim report on Mississippian Arroyo Penasco Formation of north-central New Mexico', 1967]. AAPG Bulletin ; 53 (7): 1518–1519. doi:
Baltz (ibid., p. 1508-1518) generally refuses to accept age determinations, based on microfossils, for his lithic units in the Sangre de Cristo Mountains. The age determinations and their effect on the regional correlations are discussed briefly.