Miocene-Pliocene volcanic rocks of the Nova Formation and Darwin Plateau near Death Valley, California, were erupted during extensional faulting and range in composition from basalt to rhyolite. Petrographic evidence, including sieved plagioclase, glass-bearing plagioclase, mafic and felsic xenoliths, and quartz, sanidine, and amphibole xenocrysts in samples of intermediate composition, suggest that they were derived through magma mixing or crustal assimilation. Chemical modeling indicates that rocks that show these disequilibrium textures can be derived through a combination of mixing between end-member basalt and rhyolite and fractionation of olivine, pyroxene, and plagioclase ± intergrown magnetite and ilmenite ± Cr-Al spinel. Pb and Sr isotopic data support these conclusions and may constrain the source of the contaminant to the lower crust. The age (~4 Ma) and chemical similarity of rocks from Pinto Peak and Darwin Plateau and the apparent lack of vents and feeder dikes at Pinto Peak indicate that the lavas from these two areas probably shared a common source located at Darwin Plateau. This suggests that the two areas, now separated by Panamint Valley, were adjacent during the period of volcanic activity and that Panamint Valley has therefore opened in the last 4 m.y. Volcanic activity in the study area progressed from exclusively basaltic to basaltic-andesitic-rhyolitic and shifted westward through time. These observations are consistent with a simple-shear mechanism for extension, because this mechanism better explains the “off-axis” nature of the volcanism and provides a more efficient means for crustal anatexis than a pure-shear mechanism.

Pleistocene deposits in Panamint Valley, California, document the changes in pluvial lake level, source water, and elevation of the regional groundwater table associated with climate change. The oxygen isotope stage (OIS) 2 and 6 lacustrine record is well preserved in surficial deposits, whereas the OIS 3–5 lacustrine-paludal and lacustrine record is mainly derived from an archived core sample. Amino acid racemization ratios in ostracodes and gastropods suggest that the shoreline and groundwater-discharge features that lie between ∼600 and 550 m elevation formed during one highstand, probably during OIS 6. A fossiliferous part of the ∼100-m-deep core DH-1, which was drilled in the Ballarat Basin during the late 1950s, was resampled in this study. Comparison of DH-1 with core DH-3 from Panamint Valley and core OL-92 from Owens Lake suggests the 34–78-m-depth interval of DH-1 may span all or much of OIS 4. The microfauna from this depth interval indicate a saline marsh or shallow lacustrine environment, but not a large lake. The ostracode assemblage requires low ratios of alkalinity to calcium (alk/Ca) water likely indicative of solutes in deep regional groundwater sources rather than the high alk/Ca solutes common to the Owens River system. OIS 2–aged sediment from surficial deposits, a shallow auger hole, and core DH-1 contain faunas, including the ostracode Limnocythere sappaensis , which require the high alk/Ca evolved solutes common to the Owens River. The elevation of the lacustrine sediments further indicates a moderate-sized saline lake around 180–200 m depth. In the northern Lake Hill basin, a saline lake persisted until at least 16 ka, and it was succeeded by fresh, groundwater-supported wetlands, which were fully developed by ca. 12,575 14 C yr B.P. and which persisted until around 10,500 14 C yr B.P., when the basin became a dry playa.

Abstract Glaciogenic deposits in the Death Valley region occur within the Neoproterozoic Kingston Peak Formation (Fm.). In the Panamint Range, immediately west of Death Valley, the formation is as much as 1000 m thick and is continuously exposed for nearly 100 km along the strike of the range. Although the strata are variably metamorphosed and locally exhibit pronounced ductile strain, original sedimentary textures are well preserved in many places. Diamictite occurs in two distinct intervals, a lower one comprising the Limekiln Spring and Surprise members, and an upper one, the Wildrose Sub-member of the South Park Member. Lonestones, bullet-shaped and striated clasts, and rare dropstones within these members, along with the impressive lateral continuity of diamictic units, support a glacial origin. Both diamictic intervals are succeeded by well-defined carbonates, the oldest is the Sourdough Member of the Kingston Peak Fm. and the younger one is the Sentinel Peak Member of the overlying Noonday Dolomite. The stratigraphic succession between the Sourdough Member and the Wildrose Sub-member (i.e. the Middle Park, Mountain Girl and Thorndike sub-members of the South Park Member) is c. 300 m thick and includes lithologies recording deposition in braided fluvial to platform carbonate settings. Lithostratigraphic and chemostratigraphic profiles of δ 13 C for the Sourdough (–3‰ to +2‰, increasing upward) and Sentinel Peak (–3‰ ±1‰) members suggest correlation with, respectively, the older Cryogenian (commonly referred to as ‘Sturtian’ in previous literature) and younger Cryogenian (commonly referred to as ‘Marinoan’ in previous literature) cap-carbonate sequences recognized worldwide. Potentially economic uranium deposits (secondary brannerite) occur in graphitic schist of the Limekiln Spring Member and sub-economic uranium and thorium (hosted by detrital monazite) occur within quartz-pebble conglomerate in the South Park Member. The Kingston Peak Fm. strata in the Panamint Range contain no fossils, radiometric age control or primary magnetizations.

Greenschist and amphibolite facies metamorphic rocks within the core of the Panamint Mountains of southeastern California were brought to the surface largely by movement on diachronous systems of west-dipping normal faults. Much of the unroofing can be attributed to displacement along the low-angle Harrisburg detachment, which placed weakly to unmetamorphosed upper Precambrian-Paleozoic strata on upper Precambrian metasedimentary rocks in Miocene time, prior to 10.6 ± 0.9 Ma intrusion of the Little Chief quartz monzonite porphyry. The Eastern Panamint normal fault system (late Miocene) initiated at a moderate angle (40 to 60°), juxtaposing amphibolite facies(?) Precambrian crystalline basement and upper Precambrian-Paleozoic sedimentary rocks. Range-scale anticlinal folding of the Harrisburg detachment and eastward tilting of the Eastern Panamint fault system are attributed to reverse-drag flexure induced by movement on the west-dipping Amargosa fault system (late Miocene?), which is exposed in the Black Mountains to the east of Death Valley and is inferred to dip beneath the Panamint Mountains. The low-angle Emigrant detachment (late Miocene to early Pliocene) incised the Harrisburg footwall and acted as the growth fault for the Neogene Nova Basin, which is dominated by material eroded from the metamorphic core.