Charles W. Merriam studied Paleozoic stratigraphy and paleontology of Great Basin rocks for four decades. This culminated in 1973–1974 with the publication of four important monographs on the systematics and biostratigraphy of Silurian and Devonian rugose corals in the area. Merriam died in 1974 before completing work on the Late Devonian corals and without attempting to relate his coral zones to zones based on other biologic groups.
Merriam described the rugose corals of 12 coral zones and based his age assignments almost entirely on a comparison of the Great Basin corals with those known from other areas of the world. Analysis of associated invertebrate fossils shows that some of Merriam's age assignments were in error. In this paper, we discuss the relationships of the coral zones to those based on brachiopods, conodonts, and graptolites; we assign three of Merriam's zones to the Silurian, six to the Early Devonian, and three to the Middle Devonian. Merriam designated two additional (higher) zones, but he did not describe the included corals. These two zones are noted, and lists of Great Basin rugose coral genera of Late Devonian age are presented herein to complete this review of the coral succession in a major North American area.