ABSTRACT The time interval from Supercontinent Nuna assembly in the late Paleoproterozoic to Supercontinent Rodinia breakup in the Neoproterozoic is considered by some geologists to comprise the “Boring Billion,” an interval possibly marked by a slowdown in plate tectonic processes. In northeastern Washington State, USA, similar to much of western Laurentia, early workers generally thought the tectonostratigraphic framework of this interval of geologic time consisted of two major sequences, the (ca. 1480–1380 Ma) Mesoproterozoic Belt Supergroup and unconformably overlying (<720 Ma) Neoproterozoic Windermere Supergroup. However, recent research indicates that strata considered by early workers as Belt Supergroup equivalents are actually younger, and a post-Belt, pre-Windermere record is present within the <1360 Ma Deer Trail Group and <760 Ma Buffalo Hump Formation. Thus, the northeastern Washington region perhaps comprises the most complete stratigraphic record of the “Boring Billion” time interval in the northwestern United States and holds important insights into global Proterozoic supercontinent tectonic processes. In light of these exciting developments, this field guide will address the early historic economic geology and original mapping of these Proterozoic sequences in the northeastern Washington region, and from that foundation explore more recent isotopic provenance data and their regional to global context. Finally, the guide will end with a discussion of remaining questions with a goal of stimulating interest in these relatively understudied, yet important, rocks.

Abstract The Yellowstone Geoecosystem ( Smith and Siegel, 2000 ; Morgan, 2007 ) comprises an amazing diversity of geologic features that control the character and distribution of geothermal features and soils of this landscape. The underlying bedrock geology of Yellowstone National Park (YNP) includes: Precambrian basement along the northern margin of the Park, with both low-grade metasedimentary rocks (biotite-andalusite-staurolite schists, quartzites and banded iron formations) and late Archean granitoid rocks. Phanerozoic sedimentary rocks in the northwestern corner of the Park in the southern Gallatin Range, that includes notably the Mississippian Madison Limestone near Mammoth Hot Springs, and Cretaceous shales and sandstones of the Kootenai, Eagle, Frontier and Harebell formations, south of Gardiner. The voluminous Eocene Absaroka Volcanics dominantly consisting of andesitic flows, tuffs, volcaniclastic rocks and hypabyssal intrusions. The iconic caldera-forming eruptive rocks of the Tertiary Huckleberry Ridge Tuff (2.1 Ma), Mesa Falls Tuff (1.2 Ma), and Lava Creek Tuff (0.61 Ma) of dominantly rhyolitic composition, and the post-caldera rhyolites (Christansen, 2001). The surficial geology of YNP ( Good and Pierce, 1996 ) additionally involves complex interactions of glacial geology ( Pierce, 1979 ) and active tectonics ( Pierce et al., 2007 ; Smith references). Tertiary volcanism and associated hydrothermal activity are directly related to the elevated hot spot that formed the regional Snake River Plain-Yellowstone system ( Smith and Siegel, 2000 ). Yellowstone contains the greatest number and diversity of geothermal systems on the planet, yielding an extensive array of extreme high-temperature environments, many of which are colonized by microorganisms that play either