The Zia Sand was named and described by Galusha (1966), who presented a summary of field work in the Zia Sand by Frick Laboratory parties under his direction. Rocks included in the formation are partly, but not entirely, the same as those included in the Lower Gray Member of the Santa Fe Formation by Bryce and McCann (1937). Galusha and Blick (1971) summarized previous publications on rocks assigned to the Zia Sand. On biostratigraphic evidence, they excluded from the formation several exposures Bryan and McCann (1936) and Spiegel (1961) included in or correlated with the Lower Gray Member. Manley (1978) redefined the Zia Sand to. include the overlying rocks Galusha regarded as an unnamed unit or units equivalent in age to, but lithologically distinct from, the Tesuque Formation of the Santa Fe Group, in the Espanola basin. Kelley (1977) likewise combined the Zia Sand with the overlying units, retaining the name Zia for eolian sands.
These revisions are rejected here; the limits of the Zia Sand used are very nearly those set by Galusha, in publications (1966; Galusha and Blick, 1971) and in the records of the Frick Laboratory. The rocks equivalent in age to the Tesuque Formation should receive further study and separate names. The Zia Sand as used here is a distinct depositional sequence. Galusha excluded the Zia Sand from the Santa Fe Group; other authors have included it. This paper does not attempt to resolve the question.