Named for Cerro de Muleros which is original name for Cerro de Cristo Rey. Type section is in SE1/4 SE1/4 NE1/4 sec 16, T29S, R4E, Dona Ana Co, NM, Orogrande basin. Best exposures are on north and east sides of Cerro de Cristo Rey intrusion, Dona Ana Co, NM and Chihuahua, NM. At type, Muleros is 106 ft thick; consists of 65 ft-thick lower unit of irregularly bedded, nodular, argillaceous, medium- to olive-gray, very fossiliferous limestone characterized by TEXIGRYPHAEA WASHITAENSIS; 16 ft-thick medial unit of olive gray shale interbedded with yellowish-brown, thinly bedded siltstone; and 25 ft-thick upper unit of interbedded light- olive gray shale and fossiliferous, nodular, olive-gray limestone containing abundant TEXIGRYPHAEA WASHITAENSIS. Conformably overlies Smeltertown Formation (new); conformably underlies Mesilla Valley Shale (new) with gradational contact. Geologic maps; cross sections; chart comparing nomenclature used in area. Equivalent to unit 5 of Bose (1910, Inst. Geol. Mexico, Bol. 25). Early Cretaceous (late Albian, Comanchean) age based on fossils (listed) as recorded by Bose (1910).

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