The Central and Eastern Snake River Plain is a bimodal volcanic province formed by migration of the North American Plate westward over the Yellowstone Hot Spot. Volcanic units consist of rhyolitic flows and ash fall deposits with basaltic flows originating from eruptive and volcanic centers mainly known as the Bruneau-Jarbidge, Juniper Mountain-Owyhee, Owyhee-Humboldt, and Twin Falls volcanic centers. Chapter 1 presents the Central Snake River Plain volcanic province introducing sample locations where zircon populations occur from the Archaen to the Pleistocene periods. Modern stream signatures and drainage development are discussed. Chapter 2 addresses Snake River Plain rhyolites presenting volcanic progression, tectonic associations, and petrology. Chapter 3 presents details on Miocene tuff deposits belonging to the McMullen Creek Tuff. Chapter 4 discusses the transition from ash flow to voluminous lava flow activity in the Bruneau-Jarbidge eruptive center. Chapter 5 presents pre- and post- Juniper Mountain Volcanic Center conditions of rhyolitic, tuffaceous, and basaltic compositions. Chapter 6 presents basaltic units of the Bruneau-Jarbidge and Twin Falls regional areas. Chapter 7 begins the Eastern Snake River Plain discussion providing an overview of the provincial geology. Chapter 8 discusses Eastern Snake River Plain extension and subsidence including basin and range faulting and basin infilling. Chapter 9 presents Quaternary evolution of tholeiitic basalt eruptive centers. This chapter concludes Part I of a two part series on the ESRP. Part II presents a field excursion leading to Craters of the Moon National Monument, through the national monument, and introduces volcanics associated with the Great Rift of Idaho.

The Western Snake River Plain trends northwest and is considered to be a fault bounded depression with normal faults forming major segments along both edges of the plain. Lacustrine sediments occur above thick basaltic sequences with some inter-bedded sediments mixed with basalt flows. The Western Snake River Plain and the Nevada rift developed as a continuous rift 17 million years ago. The WSRP upper crust was thinned or pulled apart as major extension began about 17 million years ago and the resulting depression was filled with up welling basalt and debris from the adjoining highlands. Chapter 1 presents an overview of the Snake River Plain as a product of the Yellowstone Hot Spot Theory. Features of each segment are described. Chapter 2 discusses the geophysics and tectonics of the SRP providing an overview and geologic setting of the western, central, and eastern SRP. Chapter 3 begins the discussion of the Western Snake River Plain addressing the geologic setting of structure and tectonics, sedimentation, and lacustrine sequences. Chapter 4 discusses the origin and evolution of the WSRP dealing with stratigraphy and volcanic units, structural faulting, and geochemistry. Chapter 5 presents a field trip discussion involving a cross sectional trace through the WSRP starting in the Owyhee Mountains extending into the Boise foothills. Ten stops are presented.

Lava flows and river deposits contemporaneous with entrechment of the Snake River canyon indicate drainage changes that provide a basis for improved understanding of the late Pleistocene history.