Named as lowermost of two members of Zia Sand for Canyada Piedra Parada, which drains type section of Zia Sand, secs 11, 14, and 23, T14N, R1E, Sandoval Co, NM in San Juan basin; type section of Piedra Parada is designated as lower 400 ft of Zia section. Overlies a greenish clay 30 ft thick tentatively assigned to Galisteo Formation (revised) unconformably; underlies Chamisa Mesa Member (new) of Zia unconformably. Unquestioned Galisteo underlies the green clay. Latter obscure unconformity may mark approximately the upper limit of the beds that produced a fauna equivalent to that of Harrison Formation of Arikaree Group of the Great Plains. Age classification of Piedra Parada is, therefore, late Arikareean (early Miocene). Consists of (descending): a 100-ft-thick set of coarse gray sand beds characterized by very large concretionary masses and ledges. Below this are variously colored sand beds, a few sandstone ledges, and, at base, brown silt, clay, sand, and a 5- to 10-ft-thick bed of pebbles. Vertebrate fossils listed. Measured section.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is the basal member of Zia Sand in Sandoval Co, NM, San Juan basin. Measured type section in secs 11, 14, 23, T14N, R1E shown in cross section. Geologic map. Unconformably overlies Galisteo Formation. Unconformably underlies Chamisa Mesa Member of Zia. Began as a widespread sheet of alluvium, grading from conglomerate at base through pebbly sand to sand. These basal sands were buried by eolian sand of upper part. Of latest Arikareean, Miocene age.

Source: GNU records (USGS DDS-6; Denver GNULEX).