New Geologic Map—Heelfly Creek Quadrangle


Title: Preliminary geologic map of the Heelfly Creek quadrangle and adjacent parts of the Tent Mountain, Soldier Peak, and Secret Valley quadrangles, Elko County, Nevada
Author: Seth M. Dee, Gregory M. Dering, and Christopher D. Henry
Year: 2015
Series: Open-File Report 15-4
Format: plate: 31 x 33 inches, color; text: 5 pages, b/w
Scale: 1:24,000

A 1:24,000-scale geologic map of the Heelfly Creek 7.5-minute quadrangle and adjacent parts of the Tent Mountain, Soldier Peak, and Secret Valley quadrangles, Elko County, Nevada. The map area covers the westernmost part of the East Humboldt Range, foothills west of the range front, and lowlands of Starr Valley. The quadrangle is traversed by numerous creeks flowing from the high topography in the east across lowlands occupied by ranching and farming communities toward the Humboldt River. New mapping has been integrated with data from previous bedrock and neotectonic studies to elucidate the structural and stratigraphic framework of the region. The relative timing and varying modes of Cenozoic extension documented here provide context for seismic hazard assessment as well as hydrocarbon and metallic mineral exploration.

Middle Proterozoic through Devonian sedimentary and metamorphic rocks (Ely Formation, Diamond Peak Formation, Guilmette Formations, Eureka Quartzite, Horse Creek assemblage and Proterozoic crystalline basement) are exposed along the high relief East Humboldt range front. These rocks are part of the Ruby Mountains–East Humboldt Range metamorphic core complex, a package of complexly deformed Proterozoic orthogneiss interfolded with Paleozoic metasedimentary rocks exhumed from mid-crustal depths along several low-angle faults during Tertiary extension. The crystalline and Paleozoic sedimentary rocks of the East Humboldt Range front are juxtaposed against middle Miocene sedimentary and volcanic rock along a north-striking, high-angle normal fault. The fault is locally buried by a mega-landslide deposit of presumed mid-Pleistocene age. Activity on this fault likely ended in the middle Pleistocene when uplift stepped 4–5 km west to the currently active frontal fault trace. Late Quaternary uplift along the active frontal fault trace exposed a section of largely northeast-dipping tuffaceous sandstone, shale and conglomerate of the Miocene Humboldt Formation. The stratigraphically lowest Cenozoic deposits, exposed near the southern map boundary in a broad anticline, may be as old as Eocene and equivalent to the Elko Formation. The Miocene sediments are locally overlain by coarsely porphyritic lavas chemically correlated with Jarbidge Rhyolite, which is widely distributed across northeastern Nevada.

Quaternary deposits in the map area include numerous inset Pleistocene surfaces beveled onto the Miocene sediments, early Pleistocene to Tertiary lacustrine and fluvial basin deposits, glacial outwash likely from the Lamoille and Angel Lake glaciations, and several inset late Pleistocene through Holocene alluvial fan and fluvial terrace deposits. Repeated late Quaternary surface-rupturing earthquakes along the active trace of the frontal fault system are recorded by increased uplift of Quaternary surfaces as a function of relative age.

This map was prepared with support from the Nevada Division of Minerals.

View or purchase Open-File Report 15-4 here:

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