Wes Hildreth (Former Employee)

The McGee Till is an early Pleistocene glacial diamict as thick as 50 m, preserved over an area of 1.65 km2 on a relict low-relief Pliocene plateau that stands 900 m higher than mouths of its bounding canyons, on the rangefront of the Sierra Nevada. Although recognized 90 years ago as the oldest till in the Sierra, its age and relation to the next oldest Sierran till have remained...

Geologists recognize lavas and ash deposits from about 60 past eruptions in the area around Mammoth Mountain and Devils Postpile, California. This raises the unanswerable question, “When will it erupt again?” An alternative, answerable, and informative question is, “How often has it erupted?” In the Mammoth Lakes Sierra, geologists have mapped in great detail all the lavas and ash...

New mapping, geochemistry, and argon geochronology illuminate a brief, remarkably silicic episode set in a mafic segment of the Cascade arc. Middle Sister was constructed during a 35-k.y. episode in the late Pleistocene from mafic, intermediate, and silicic eruptions adjacent to the primarily rhyolitic South Sister. Eruptions in the Three Sisters volcanic cluster prior to 50 ka were...

Paleomagnetic data for samples collected from outcrops of basaltic spatter at the Ubehebe Crater cluster, Death Valley National Park, California, record a single direction of remanent magnetization indicating that these materials were emplaced during a short duration, monogenetic eruption sequence ~ 2100 years ago. This conclusion is supported by geochemical data encompassing a narrow...

Recent improvements in analytical and microsampling techniques for multiple geochronometers have resulted in datasets with unprecedented temporal and spatial resolution. These advances are accompanied by the discovery of crystal- and outcrop-scale complexities previously obscured by low analytical precision. Single-crystal incremental heating resolves subtle, intracrystal isotopic...

This guide to the geology of Long Valley Caldera is presented in four parts: (1) An overview of the volcanic geology; (2) a chronological summary of the principal geologic events; (3) a road log with directions and descriptions for 38 field-trip stops; and (4) a summary of the geophysical unrest since 1978 and discussion of its causes. The sequence of stops is arranged as a four-day...