Abstract Rocks in the major roof pendants of the eastern Sierra Nevada have been mapped in various degrees of detail to better understand their stratigraphy, internal structure, and geologic history, and their relationships to other rock assemblages in the region. Ten formations ranging in age from Middle(?) Cambrian to Middle(?) Permian are recognized in these pendants, which along with other minor pendants, constitute a tectonostratigraphic unit called the Morrison block . Rocks of the Morrison block were first deformed by north-northwest-trending thrust faults and footwall syn-clines involving strata as young as Early or Middle Permian. We designate this event, which correlates with a similar pre-middle Early Triassic event recognized in rocks near Tinemaha Reservoir, the Morrison orogeny. Structures produced during this orogeny include a probable cryptic thrust fault separating rocks assigned to the Morrison block from those in the Big Pine Creek pendant, which may belong to the White-Inyo block, and the Nevahbe thrust, which separates lower from upper Paleozoic rocks in the eastern part of the Mount Morrison pendant and may separate the Pine Creek and Bishop Creek pendants. In the Mount Morrison pendant structures produced during the Morrison orogeny apparently were later refolded twice prior to sinistral displacement on the Laurel-Convict fault, which cross-cuts older structures and is intruded by a pre-latest Late Triassic dike . Other thrust faults in the eastern Sierra Nevada include the Golconda thrust of early Middle Triassic age and the Lundy Canyon thrust of Late Triassic age. The Golconda thrust system apparently overprints the Roberts Mountains thrust and separates rocks of the Morrison block from those of the Golconda and Roberts Mountains allochthons in the Saddlebag Lake pendant, and perhaps from those of the Roberts Mountains allochthon in the Northern Ritter Range and Log Cabin Mine pendants . After thrust-faulting, but prior to intrusion of the Late Triassic Wheeler Crest Granodiorite, dextral movement on the Tinemaha fault displaced Paleozoic facies and structural belts in the Sierra Nevada northward, producing most of the present complicated paleogeographic patterns apparent in the region. Other less important structures, such as the Laurel-Convict fault, have further complicated the geology of the Morrison block .

Abstract Long Valley Caldera and the Mono–Inyo Domes volcanic field in eastern California lie in a left-stepping offset along the eastern escarpment of the Sierra Nevada, at the northern end of the Owens Valley and the western margin of the Basin and Range Province. Over the last 4 Ma, this volcanic field has produced multiple volcanic eruptions, including the caldera-forming eruption at 760 000 a BP and the recent Mono–Inyo Domes eruptions 500–660 a BP and 250 a BP . Beginning in the late 1970s, the caldera entered a sustained period of unrest that persisted through the end of the century without culminating in an eruption. The unrest has included recurring earthquake swarms; tumescence of the resurgent dome by nearly 80 cm; the onset of diffuse magmatic carbon dioxide emissions around the flanks of Mammoth Mountain on the southwest margin of the caldera; and other indicators of magma transport at mid- to upper-crustal depths. Although we have made substantial progress in understanding the processes driving this unrest, many key questions remain, including the distribution, size, and relation between magma bodies within the mid-to-upper crust beneath the caldera, Mammoth Mountain, and the Inyo Mono volcanic chain, and how these magma bodies are connected to the roots of the magmatic system in the lower crust or upper mantle.