Abstract The distribution of Middle and Late Proterozoic sedimentary and metasedimentary cover that lies unconformably on Early Proterozoic and Archean crystalline basement has been known for decades, but recent work, employing techniques of paleomagnetic correlation, sedimentology, sequence stratigraphy, and analysis of tectonic subsidence has led to modifications of some long-accepted correlations and tectonic models. Within the context of both older classical studies and this new work, the stratigraphy, correlation, tectonic setting, fossil content, and mineral potential of Middle and Late Proterozoic rocks of parts of the Rocky Mountain, Colorado Plateau, and Basin and Range provinces of the United States are discussed. A problem common to interpretation of all Proterozoic strata is a widespread lack of fossil control on age and paleoecology, which makes correlations inherently uncertain and interpretation of depositional environments more difficult. We present current hypotheses about these topics and stress the uncertainty of some of our conclusions. The apparent polar wander path for the North American craton, as derived from the Middle and Late Proterozoic sedimentary cover, is central to our modifications of stratigraphie correlation, especially of Middle Proterozoic rocks. The reader is asked to view the work and summaries presented here in the light of ongoing scientific debate about strata that are chronically stubborn in yielding information. The authors of sections of this chapter include both those who have performed classical studies, which are the foundation of our present understanding, and younger geologists who have been busy refining and modifying early interpretations, using different methods of study. The treatment in this chapter is therefore variable depending on which generation of investigators is speaking.

Abstract Nearly continuous successions of late Proterozoic through Upper Devonian rocks are widespread in the western United States between the structural fronts of the Sevier and Sonoma orogens (Plates 2-1 to 2-6, 3-1 to 3-4). West of the Sonoma orogenic front in Washington, Oregon, northe Rn and southe Rn California, western Idaho, and western Nevada, rocks of this age are limited to many small areas of exposures, most of which are shown on Plate 3-5. East of the Sevier orogenic front, some large areas on the cratonic platform contain only partial stratigraphic records because of eithe R nondeposition or erosion. The western limit of mapped carbonate-shelf rocks can be obtained from only a few tectonic windows because those rocks disappear beneath thrust plates of western facies rocks of the same age or of younger and older rocks that moved eastward as much as 200 km or more during the Antler and later orogenies. Figure 1 shows Devonian and older paleotectonic features, major post-Devonian faults, and locations of the 12 generalized stratigraphic columns shown in Figure 2.

Abstract The Whetstone Mountains are in southeastern Arizona along the boundary between Cochise and Pima Counties, about 42 mi (70 km) southeast of Tucson (Fig. 1), Benson, 15 mi (25 km) to the northeast, and Sierra Vista, about the same distance to the south, are the nearest towns. Most of the Whetstone Mountains, including the Dry Canyon area, are in Coronado National Forest. Dry Canyon, on the lower southeast flank of the mountains, is in the Benson15-minute Quadrangle and the Apache Peak and McGrew Spring 7½-minute Quadrangles. Along the canyon, and particularly on the ridge on its south side, a thick sequence of paleozoic rocks is exposed, which is the focus of this report. The Dry Canyon area (Fig. 2) is reached via Arizona 90, which trends south toward Fort Huachuca and Sierra Vista from its junction with I-10, about 2.7 mi (4.5 km) west of Benson. At a point 13 mi (21.5 km) south of 1–10, a dirt road, marked by a simple ranch gate, leads westward a few mi (km) across public land into Dry Canyon. This road is best traveled using a four-wheel-drive vehicle, but it was passable with difficulty for passenger cars in 1982.