Mafic Volcanism and Environmental Geology of the Eastern Snake River Plain, Idaho

Geology presented in this field guide covers a wide spectrum of internal and surficial processes of the eastern Snake River Plain, one of the largest components of the combined late Cenozoic igneous provinces of the western United States. Focus is on Quaternary basaltic plains volcanism that produced monogenetic coalescent shields, and phreatomagmatic eruptive centers that produced tuff cones and rings. These dominant systems are compared to compositionally evolved polygenetic eruptive centers and silicic domes that represent an extended range of petrologic processes. Selected non-volcanic features are included to illustrate the importance of stream runoff, eolian sediment, the Snake River Plain aquifer and seasonal fires on the ecology of this region. The guide is constructed in two parts, beginning with an overview of the geology followed by road directions, with explanations, for specific locations and possible side trips. The geology overview section briefly summarizes the collective knowledge gained, and implications made, over the past few decades. The road guide mainly covers plains volcanism, lava flow emplacement, basaltic shield growth, phreatomagmatic eruptions, and complex eruptive centers. Locations and explanations are also provided for environmental topics associated with the region, such as geohydrology, groundwater contamination, range fires and cataclysmic floods.