ABSTRACT: At New Well Peak in the Big Hatchet Mountains of southwestern New Mexico, a well-exposed, nearly homoclinal, and almost complete section of the Pennsylvanian–lower Permian (Cisuralian) Horquilla Formation is ~1-km thick, rests with erosional disconformity on the Mississippian Paradise Formation, and its top is covered. Nearby outcrops indicate that the lower Permian Earp Formation rests disconformably on the Horquilla Formation. At the New Well Peak section the Horquilla Formation comprises three lithologically distinct members named here: 1) lower, Bugle Ridge Member of sandy limestones, calcarenites, and oolitic grainstones, ~100-m thick; 2) middle, New Well Peak Member of cherty, thick-bedded limestones, many with silicified Chaetetes, ~600-m thick; and 3) an upper, Sheridan Canyon Member of thin-bedded limestones, cyclically interbedded with shales that have especially rich fusulinacean assemblages, ~350-m thick. The only significant structural disruption of the Horquilla Formation at the New Well Peak section occurs low in the New Well Peak Member in the form of a complex of down-to-the-north normal faults (New Well Peak fault zone), topographically low on the north side of New Well Peak. Fusulinid and conodont biostratigraphy indicates that most of the Bugle Ridge Member is Morrowan, and the upper part is Atokan. The New Well Peak Member is Atokan-Missourian, and the Sheridan Canyon Member is Missourian-Wolfcampian. Newly collected conodont data allow correlation of Atokan-Wolfcampian fusulinid and conodont biostratigraphy at New Well Peak, thus providing an important Pennsylvanian-lower Permian reference section for the integration of these two microfossil groups.