Univ. Nevada Bull., v. 27, no. 3, p. 15. Hales limestone. Almost wholly limestone, of bluish-gray color, thin-bedded but with a few massive members; near base lenses and nodules of chert; at base about 50 feet of brown shaly limestone transitional from calcareous slates of underlying Tybo shale; in places these transitional slates are absent; in upper part of formation are one or more beds of quartzite, one of which is 200 feet thick. Thickness of formation 3,000+/- feet. Named for Hales shaft of Tybo Mine, northern Nye County, central Nevada, which is almost entirely within this formation. Few scanty fossils below the quartzites are pronounced by Resser to probably all be Upper Cambrian. Overlain by Pogonip limestone in Tybo district. Grades into overlying and underlying formations.

Source: US geologic names lexicon (USGS Bull. 896, p. 896).