Named as lowermost of four members of Ely Springs Dolostone (redescribed). Type section in Barn Hills in Confusion Range, about 2 mi north northwest of Ibex Well bench mark 4779 [for which unit probably named], in SE1/4 NW1/4 sec 26, T21S, R14W, western Millard Co, UT. Additional exposures in northwestern UT at Silver Island Mountain and eastern NV at southern Egan Range, Delamar Mountains and Cherry Creek Range. Unit occurs in Great Basin province. Consists of grayish-black to medium-gray or brownish-black, microcrystalline to very finely crystalline dolostone; thin to thick bedded; weathers from dark gray to brownish gray. Thickness at type is 31 ft; averages about 28 ft. Overlies Eureka Quartzite; underlies Barn Hills Member (new) of Ely Springs. Measured sections. Fossil corals indicate early Late Ordovician ("late Trenton") age.

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