Prepared in conjunction with the 2022 GSA Cordilleran/Rocky Mountain Sections Joint Meeting, this Field Guide showcases trips to geologically interesting areas in Arizona, Nevada, and California. Enjoy a three-day trip to the Buckskin-Rawhide and northern Plomosa Mountains metamorphic core complexes in Arizona. In Nevada, learn about the geology of Frenchman Mountain and Rainbow Gardens and landslide deposits and mechanisms in the eastern Spring Mountains. Or learn about microbialites in Miocene and modern lakes near Las Vegas. When weather permits, unravel the geological history of southern Death Valley, and explore vertebrate paleontology and Cenozoic depositional environments in Death Valley, California.

ABSTRACT Large-scale landslide deposits (covering >1 km 2 ) are prevalent throughout the Basin and Range province. However, their presence and importance in the evolution of the Basin and Range remain poorly recognized. On this field trip, we will visit four landslide deposits along the eastern flank of the Spring Mountains on the western margin of Las Vegas Valley. The first half of the day will be spent looking at vertical and lateral textures within the Blue Diamond landslide deposit, which mostly caps hills and ridges between the southern ends of the Wilson Cliffs and Blue Diamond Hill. We interpret this deposit as having a two-phase emplacement, with an initial rock avalanche emplacement onto Blue Diamond Hill, followed by failure as a rock compound landslide along weak gypsum layers in the Kaibab Formation. During the second half of the day, we will visit a smaller rock avalanche deposit (La Madre), a large rock compound slide that resulted from failure of the northern flank of Blue Diamond Hill (Red Rock Wash), and a large block of Paleozoic rock that likely was emplaced as either a rock compound slide or a rock planar slide (Lone Mountain).

Abstract There is a long history of debate over glacial versus non-glacial interpretations of both Quaternary and pre-Quaternary diamicts in various places around the world, and the Spring Mountains in southern Nevada are the site of one such debate. Here the debate focuses not only on Quaternary diamicts, but also on landforms and erosional features. The deposits and geomorphic features in question will be examined on this field trip. The Spring Mountains are developed in a fault block in the southern Basin and Range Province; elevations range from ~4000 ft (1220 m) at the eastern base to 11,918 ft (3634 m) at Charleston Peak. The range is farther south than any other glaciated range in Nevada; however, the glaciated San Gorgonio Mountains on the border of the Basin and Range in California are farther south, though in a much more maritime position. The Spring Mountains lie in the rain shadow of the Sierra Nevada; rainfall increases from ~4 in (10 cm) per year in the Las Vegas Valley to ~20 in (50 cm) per year at the crest of the range. A published interpretation of sedimentary and geomorphic features at the head of Kyle Canyon claims that steep valley heads of Kyle Canyon and Big Falls wash are degraded cirques, that a ridge at the mouth of Big Falls wash is a lateral moraine, and that diamicts exposed in the ridge include glacial till. An alternative view is that the “cirques” are normal valley heads as are found in high-relief desert ranges, that the “lateral moraine” owes some of its ridge character to erosion along Big Falls wash and may originally have been a debris flow levee or a protalus rampart, and that the “till” is actually colluvium. Abundant clast striations constitute a key element of the glacial interpretation, and much rests on whether glacial striations can be distinguished from mass movement striations.