Newly recognized cyclomedusoid fossils in the Antelope Mountain Quartzite confirm that it is latest Neoproterozoic (Ediacaran) in age. Biogeographic affinities of the cyclomedusoid fossils suggest that the Yreka subterrane and its close associate, the Trinity subterrane, formed after the breakup of Rodinia in an ocean basin bordering Australia, northern Canada, Siberia, and Baltica. Reevaluating biogeographic, geological, and paleomagnetic evidence in the context of this starting point, the Yreka subterrane and Trinity subterrane may have been located at either 7°N or 7°S latitude ca. 580–570 Ma, but were not necessarily close to Laurentia. Continental detrital zircons (3.2–1.3 Ga) in the Antelope Mountain Quartzite most likely came from Australia or Siberia rather than Laurentia. The Yreka subterrane and Trinity subterrane record ∼180 m.y. of active margin events somewhere in Panthalassa (Proto-Pacific Ocean). Paleozoic biogeographic data, paleomagnetism, and regional relationships indicate that Yreka subterrane and Trinity subterrane were located throughout the early Paleozoic in the part of Panthalassa surrounded by Australia, NW Laurentia, Siberia, China, Baltica, and the Uralian terranes. By the mid-Devonian they were located at 31°N or 31°S in a somewhat isolated location, probably in a Northern Hemisphere oceanic plateau or island chain well outboard of other tectonic elements, and by the Permian they were almost completely isolated from other tectonic elements. The Yreka subterrane, as part of the Klamath superterrane, was not native to North America and did not accrete to it until the Early Cretaceous.

Study of Late Triassic biofacies and associated paleoecology reveals new silicified shallow-water corals and other fossils from new and previously known localities within the Alexander terrane (Keku Strait and Gravina Island, southeast Alaska) and Wrangellia (Wrangell Mountains, Alaska, and Vancouver Island, British Columbia). Twenty-five species of coral are identified from eight localities within the Alexander terrane and 34 species are identified from four localities in Wrangellia. Distributions of silicified shallow-water marine fossils contribute to Late Triassic (Norian–Rhaetian) paleoecology, biotic diversity, and terrane paleogeography. Depositional environments establish the conditions in which these organisms lived as well as provide evidence for lithological correlation between tectonically separate fragments. This study also confirms the presence of biostrome reef buildups in the southern Alexander terrane (Gravina Island), indicating warm, clear, and nutrient-free water with lots of sunlight; this differs from the central Alexander terrane (Keku Strait) and northern Wrangellia (Wrangell Mountains), where corals grow as individual colonies, not in a structured, reef-like buildup, and are accompanied by filter- and detritus-feeding organisms indicating warm, cloudy and nutrient-rich water in a back-reef environment. Paleobiogeographic results from silicified Upper Triassic corals show faunal similarity between Gravina Island and Keku Strait (Alexander terrane) and no similarity between northern and southern Wrangellia. Likewise, no similarity was found between the Alexander terrane and either northern or southern Wrangellia.

The Upper Triassic (Carnian–Norian) Martin Bridge Formation of northeastern Oregon, southeastern Washington, and western Idaho is characterized by rapidly shifting depositional processes within a tropical volcanic island arc setting. Martin Bridge sequences in the Hells Canyon and northern Wallowa Mountains document shallow-water peritidal evaporitic sediments that are succeeded by deeper and predominantly subtidal deposits. This indicates drowning of the carbonate platform and a transition to deeper-water turbiditic sedimentation before a late Triassic transition into the overlying mid-Norian to Jurassic Hurwal Formation. At the type locality in the southern Wallowa Mountains, dysaerobic shales, carbonate debris sheets, and turbiditic sediments indicate distal slope and basinal environments while other facies at other sites in the Wallowa Mountains and Hells Canyon areas indicate reef and shallow-water platform settings. In this paper we formally recognize the name Martin Bridge Formation and reinstate the type locality in the southern Wallowa Mountains as the principal unit strato-type. An additional reference section is given at Hurricane Creek in the northern Wallowa Mountains. The Martin Bridge is formally divided into four members: the Eagle Creek and Summit Point Members are introduced and formally proposed herein and the BC Creek and Scotch Creek Members also are elevated to formal status. A partial reconstruction of the Wallowa terrane during deposition of the Martin Bridge Formation suggests a north-south (or northeast-southwest) trending platform margin facing a forearc basin situated to the east (or southeast). The lithofacies and paleontological characteristics of the Martin Bridge can be put into the framework of a depositional and a tectonic model to help better explain many of the stratigraphic and paleontologic problems previously encountered. We believe that the Wallowa terrane provides one of the best and most complete examples yet known for shallow-water carbonate depositional patterns in an oceanic island arc setting.