Homedale Volcanic Field

Homedale Volcanic Field
Name	Homedale Volcanic Field
Location	Owyhee County, Idaho, United States
Type	volcanic field
Age	Pleistocene–Holocene
Last eruption	Holocene (uncertain)

Homedale Volcanic Field is a volcanic field in southwestern Idaho near the Oregon border characterized by Quaternary basaltic to basaltic-andesitic vents, lava flows, and cinder cones. The field lies within a complex regional mosaic that includes continental rift, back-arc, and hotspot-related volcanic provinces; it is proximate to several Owyhee County, Idaho landmarks and transportation corridors. The volcanic field's dispersed vents and varied eruption styles make it significant for studies comparing Snake River Plain volcanism, Columbia River Basalt Group stratigraphy, and Basin and Range tectonics.

Geology

The geology of the Homedale area integrates stratigraphic units and structures documented across Oregon–Idaho borderlands, including Miocene flood basalts of the Columbia River Basalt Group, widespread deposits related to the Bruneau-Jarbidge volcanic field, and Quaternary sediments overlain by Holocene lavas. Regional mapping connects the field to structural features mapped by the United States Geological Survey and state geological surveys in Idaho and Oregon, and to geomorphic surfaces correlated with glacial and fluvial events in the Craters of the Moon National Monument and Preserve region. Lithostratigraphic relationships show interaction between basin-fill sediments attributable to the Great Basin and extrusive products correlated by geochronology with eruptions recorded in the Snake River Plain.

Volcanoes and Vents

The field contains numerous discrete vents including cinder cones, spatter cones, and shield-like edifices aligned along local faults and fissures mapped in Owyhee County. Notable nearby volcanic centers used as comparative references in the literature include Newberry Volcano, Steens Mountain, and vents associated with the McDermitt Caldera. Cones and fissures are distributed near the towns of Homedale, Idaho, Marsing, Idaho, and along corridors toward Vale, Oregon, and have been plotted in inventories maintained by the USGS National Volcanic Database and regional universities.

Eruptive History

Eruptive episodes span late Pleistocene into the Holocene with radiometric ages and tephrochronology correlated to regional markers such as deposits linked to Bonneville Flood stages and ash layers tied to Mount St. Helens and Mount Mazama events. Field relations suggest multiple, monogenetic eruptions producing lava flows that traveled across preexisting basaltic plains and ponded against paleotopographic highs. Comparative studies reference eruptive sequences from Medicine Lake Volcano and basaltic sequences on the Columbia Plateau to constrain eruption rates and recurrence intervals for this volcanic field.

Petrology and Geochemistry

Lavas and pyroclastics from the field are predominantly mafic, ranging from olivine tholeiite basalts to more evolved basaltic andesites; mineral assemblages commonly include olivine, clinopyroxene, plagioclase, and rare amphibole. Whole-rock major- and trace-element patterns and isotopic signatures have been compared to suites from the Snake River Plain and Central Oregon volcanic provinces to infer mantle source heterogeneity, crustal assimilation, and degrees of partial melting. Geochemical datasets used for interpretation draw on methods standardized by laboratories affiliated with institutions such as Stanford University, University of Idaho, and Oregon State University.

Tectonic Setting and Formation

Formation of the field is ascribed to the interplay of Basin and Range extension, back-arc processes related to the subduction history of the Juan de Fuca Plate, and mantle dynamics implicated in Yellowstone hotspot migration across the Snake River Plain. Structural control by NW- and NE-trending faults reflects regional stress orientations documented in seismic and geodetic studies by the USGS and state seismic networks. Plate-scale reconstructions referencing the cessation of the Farallon Plate subduction and the evolution of the Pacific Plate margin inform models for magma ascent beneath southwestern Idaho and eastern Oregon.

Volcanic Hazards and Risk

Although most eruptions were monogenetic and localized, potential hazards include future small-volume lava flows, tephra fall, and lava-juvenile gas emissions; hazards are assessed in the context of nearby population centers such as Homedale, Idaho and infrastructure including Interstate 84 (Idaho–Oregon). Volcanic hazard communication and monitoring incorporate protocols from the USGS Volcanic Hazards Program and coordination with state emergency management agencies in Idaho and Oregon. Comparative risk assessments reference hazard maps developed for similar monogenetic fields in the Pacific Northwest, including studies of eruptive impacts on agriculture and water resources in the Treasure Valley.

Human History and Land Use

Human interactions span indigenous use by tribes associated with the Nez Perce, Shoshone, and Paiute cultural territories through Euro-American settlement, ranching, and resource development in Owyhee County. Land use includes grazing, limited agriculture, recreation, and energy infrastructure, with archaeological surveys coordinated by the Idaho State Historical Society and mitigation guidelines reflecting state and federal land management agencies such as the Bureau of Land Management. Scientific investigation has involved collaborations among regional institutions including the Idaho Geological Survey and university geology departments.

Category:Volcanic fields of Idaho Category:Volcanism of the United States