New Mexico Bureau of Mines

Cenozoic sedimentary rocks could be designated as those rocks everywhere underfoot, but rarely seen or seriously mentioned. They must be drilled through in any search for oil; in many places they are the reservoir for usable groundwater; and they are the source of significant amounts of industrial minerals and rocks. Unless one attempts to split the Recent from the Cenozoic, there is no problem in designating the up-per boundary; the sky is the limit. The Cretaceous-Cenozoic boundary does pose problems, chiefly be-cause late Cretaceous and Cenozoic deposits are al-most entirely terrestrial, invertebrate faunas are sparse,floras are poorly preserved and in part not diagnostic. Similarly, the Tertiary-Quaternar