The Concha limestone of Gilluly and others, and the Rainvalley formation, herein defined, are the youngest strata of Permian age recognized in southern Arizona. The 2 formations occur in many of the outcrops of upper Paleozoic rocks in southeastern Arizona, but have not been identified W. of central Pima County, Arizona. The type section of the Concha limestone in the Gunnison Hills, Cochise County, Arizona, is incomplete, and a reference section is proposed from the Mustang Mountains. The Concha limestone is thick-bedded to massive, gray to dark gray, and very finely crystalline, and it contains numerous chert nodules, particularly in the lower 180 ft. It is 570 ft. thick at the reference locality. The Rainvalley formation conformably overlies the Concha limestone and is 390 ft. thick at the proposed type locality in the Mustang Mountains. It is made up of thin-bedded limestone and dolomitic limestone units and a few sandstone beds. The Rainvalley is separated from the Concha limestone because its beds are thinner and more varicolored and have a higher dolomite content than the thick-bedded limestone of the Concha. The age of the Concha is tentatively considered Leonard and Guadalupe(?) and that of the Rainvalley, Guadalupe(?).

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