Santa Fe Group (Neogene), Ceja del Rio Puerco, northwestern Albuquerque Basin, Sandoval County, New Mexico

-The badland escarpment of the Puerco River (Ceja del Rio Puerco) in southern Sandoval County, New Mexico exposes 410 m of Miocene sediments at the western edge of the northern Albuquerque basin. Geologic mapping and accompanying lithostratigraphic, biostratigraphic and magnetostratigraphic studies enable the Zia and overlying Arroyo Ojito formations, typified in the Jemez River region to the north, to be rec ognized in the Ceja outcrops. The Zia Formation (early Miocene) rests unconformably on nonmarine Cretaceous (Menefee Formation) strata. Most of the Zia is volcaniclastic and eolian in origin. It can be subdivided into a lower dune (Piedra Parada Member, 70 m), middle fluvial (Chamisa Mesa Member, 30 m), and an upper playa and dune facies (Caiiada Pilares Member, 75 m). These rocks are overlain with apparent conformity by the Arroyo Ojito Formation, of flu vial origin, containing minor lacustrine, and eolian bodies. The Arroyo Ojito is represented primarily by the Cerro Conejo Member (245 m, medial Miocene), which gives way conformably to the gravelly Navajo Draw Member (>30 m thick). Higher units within the Arroyo qjito Formation are seen only east of the Sand Hill fault, where they include the upper part of the Loma Barbon Member and the locally uncon formably overlying Ceja Member. Both are coarse fluviatile bodies with a varied clast composition indicating sources in mountains to the north as well as the Colorado Plateau. A basaltic diatreme (Benevides Hill) that erupted through the Zia and most of the Cerro Conejo strata predates incision of the Puerco River. The youngest deposits, the Pantadeleon Formation of Pliocene and Pleistocene age, fill local fault-angle depressions formed during continuing deformation of the basin-fill.Two prominent down-to-the-east faults of 200-300- m throw break the sedimentary column. The Moquino fault and contiguous Navajo fault have a northeastern trend con cordant with the Laramide Puerco fault zone, and show evidence of left-slip as well as syn-rift normal faulting. The Sand Hill fault to the east has a more northerly trend like the major dip-slip faults that break the deeper basin-fill.