More than 95% of the eastern Snake River Plain (ESRP) is covered by basaltic lava flows erupted in the Brunhes Normal-Polarity Chron; thus they are younger than 730 ka. About 13% of the area of the ESRP is covered by lava fields of latest Pleistocene and Holocene age <15 ka. More than 90% of the basalt volume of the ESRP is included in coalesced shield and lava-cone volcanoes made up dominantly of tube- and surface-fed pahoehoe flows. Deposits of fissure-type, tephra-cone, and hydrovolcanic eruptions constitute a minor part of the basalt volume of the ESRP. Eight latest Pleistocene and Holocene lava fields serve as models of volcanic processes that characterize the basaltic volcanism of the ESRP. The North Robbers, South Robbers, and Kings Bowl lava fields formed in short-duration (a few days), low-volume (each <0.1 km 3 ), fissure-controlled eruptions. The Hells Half Acre, Cerro Grande, Wapi, and Shoshone lava fields formed in long-duration (several months), high-volume (1 to 6 km 3 ), lava cone- and shield-forming eruptions. Each of these seven lava fields represents monogenetic eruptions that were neither preceded nor followed by eruptions at the same or nearby vents. The Craters of the Moon lava field is polygenetic; about 60 flows were erupted from closely spaced vents over a period of 15,000 years. Most of the basaltic volcanism of the ESRP is localized in volcanic rift zones, which are long, narrow belts of volcanic landforms and structures. Most volcanic rift zones are collinear continuations of basin-and-range-type, range-front faults bordering mountains that adjoin the ESRP. It is not clear whether the faults extend into the ESRP in bedrock beneath the basaltic lava flows. The great bulk of basaltic flows in the ESRP are olivine basalts of tholeiitic and alkaline affinities. The olivine basalts are remarkably similar in chemical, mineralogical, and textural characteristics. They were derived by partial melting of the lithospheric mantle at 45 to 60 km, and they have been little affected by fractionation or contamination. Evolved magmas having SiO 2 contents as high as 65% occur locally in and near the ESRP. The chemical and mineralogical variability of the evolved rocks is due to crystal fractionation in the crust and to contamination by crustal minerals and partial melts of crustal rocks. The trace-element compositions of the olivine basalts and the most primitive evolved basalts do not overlap, suggesting that the evolved rocks were derived from parent magmas that are fundamentally different from the parent magmas of the olivine basalts. The distribution and character of volcanic rift zones in the ESRP are partly controlled by underlying Neogene rhyolite calderas. Areas that lack basalt vents and have only poorly developed volcanic rift zones overlie calderas or parts of calderas filled by thick, low-density sediments and rocks, which served as density barriers to the buoyant rise of basaltic magma. Volcanic rift zones are locations of concentrated extensional strain; they define regional stress patterns in the ESRP.

Abstract The Wallowa terrane is one of five pre-Cenozoic terranes in the Blue Mountains province of Oregon, Idaho, and Washington. The other four terranes are Baker, Grindstone, Olds Ferry, and Izee. The Wallowa terrane includes plutonic, volcanic, and sedimentary rocks that are as old as Middle Permian and as young as late Early Cretaceous. They evolved during six distinct time segments or phases: (1) a Middle Permian to Early Triassic(?) island-arc phase; (2) a second island-arc phase of Middle and Late Triassic age; (3) a Late Triassic and Early Jurassic phase of carbonate platform growth, subsidence, and siliciclastic sediment deposition; (4) an Early Jurassic subaerial volcanic and sedimentary phase; (5) a Late Jurassic sedimentary phase that formed a thin subaerial and thick marine overlap sequence; and (6) a Late Jurassic and Early Cretaceous phase of plutonism. Rocks in the Wallowa terrane are separated into formally named units. The Permian and Triassic Seven Devils Group encompasses the Middle and Late(?) Permian Windy Ridge and Hunsaker Creek Formations and the Middle and Late Triassic Wild Sheep Creek and Doyle Creek Formations. Some Permian and Triassic plutonic rocks, which crystallized beneath the partly contemporaneous volcanic and sedimentary rocks of the Seven Devils Group, represent magma chambers that fed the volcanic rocks. The Permian and Triassic plutonic rocks form the Cougar Creek and Oxbow “basement complexes,” the Triassic Imnaha plutons, and the more isolated Permian and Triassic plutons, such as those in the Sheep Creek to Marks Creek chain and in the southern Seven Devils Mountains near Cuprum, Idaho. The Seven Devils Group, and its associated plutons, are capped by the Martin Bridge Formation, a Late Triassic platform and reef carbonate unit, with associated shelf and upper-slope facies, and overlying and partly contemporaneous siliciclastic, limestone, and calcareous phyllitic rocks of the Late Triassic and Early Jurassic Hurwal Formation. Younger rocks are a subaerial Early Jurassic volcanic and sedimentary rock unit of the informally named Hammer Creek assemblage, and a Late Jurassic overlap sedimentary unit, the Coon Hollow Formation. Late Jurassic and Early Cretaceous plutons intrude the older rocks. Lava flows of the Miocene Columbia River Basalt Group overlie the pre-Cenozoic rocks. Late Pleistocene and Holocene sedimentation left discontinuous deposits throughout the canyon. Most impressive are deposits left by the Bonneville flood. The latest interpretations for the origin of terranes in the Blue Mountains province show that the Wallowa terrane is the only terrane that, during its Permian and Triassic evolution, had an intra-oceanic (not close to a continental landmass) island-arc origin. On this field trip, we travel through the northern segment of the Wallowa terrane in Hells Canyon of the Snake River, where representative rocks and structures of the Wallowa terrane are well exposed. Thick sections of lava flows of the Columbia River Basalt Group cap the older rocks, and reach river levels in two places.

Abstract Basaltic volcanism in the Snake River Plain of southern Idaho has long been associated with the concept of a mantle plume that was overridden by North America during the Neogene and now resides beneath the Yellowstone plateau. This concept is consistent with the time-transgressive nature of rhyolite volcanism in the plain, but the history of basaltic volcanism is more complex. In the eastern Snake River Plain, basalts erupted after the end of major silicic volcanism. The basalts typically erupt from small shield volcanoes that cover up to 680 km 2 and may form elongate flows that extend 50–60 km from the central vent. The shields coalesce to form extensive plains of basalt that mantle the entire width of the plain, with the thickest accumulations of basalt forming an axial high along the length of the plain. In contrast, basaltic volcanism in the western Snake River Plain formed in two episodes: the first (ca. 7–9 Ma) immediately following the eruption of rhyolites lavas now exposed along the margins of the plain, and the second forming in the Pleistocene (≤2 Ma), long after active volcanism ceased in the adjacent eastern Snake River Plain. Pleistocene basalts of the western Snake River Plain are intercalated with, or overlie, lacustrine sediments of Pliocene-Pleistocene Lake Idaho, which filled the western Snake River Plain graben after the end of the first episode of basaltic volcanism. The contrast in occurrence and chemistry of basalt in the eastern and western plains suggest the interpretation of volcanism in the Snake River Plain is more nuanced than simple models proposed to date.

Abstract The Quaternary record of the Uinta Mountains of northeastern Utah has been studied extensively over the past decade, improving our understanding of the Pleistocene glacial record and fluvial system evolution in a previously understudied part of the Rocky Mountains. Glacial geomorphology throughout the Uintas has been mapped in detail and interpreted with reference to other well-studied localities in the region. In addition, studies in Browns Park and Little Hole in the northeastern part of the range have provided information about paleoflooding, canyon cutting, and integration of the Green River over the Uinta Mountain uplift. Notable contributions of these studies include (1) constraints on the timing of the local last glacial maximum in the southwestern Uintas based on cosmogenic surface exposure dating, (2) insight into the relationship between ice dynamics and bedrock structure on the northern side of the range, and (3) quantification of Quaternary incision rates along the Green River. This guide describes a circumnavigation of the Uintas, visiting particularly well-documented sites on the north and south flanks of the range and along the Green River at the eastern end.

ABSTRACT Today, the United States Department of the Interior manages 500 million acres of surface land, about one-fifth of the land in the United States. Since enactment of the Antiquities Act in 1906, historic and scientific resources collected on public land have remained government property, held in trust for the people of the United States. As a result, the Department of the Interior manages nearly 204 million museum objects. Some of these objects are in federally managed repositories; others are in the repositories of partner institutions. The establishment of the United States as a nation corresponded with the development of paleontology as a science. For example, mastodon fossils discovered at or near present-day Big Bone Lick State Historic Site, Kentucky, found their way to notable scientists both in the United States and in Europe by the mid-eighteenth century and were instrumental in establishing the reality of extinction. Public land policies were often contentious, but generally they encouraged settlement and use, which resulted in the modern pattern of federal public lands. Continued investigation for fossils from public land filled the nation’s early museums, and those fossils became the centerpieces of many museum exhibitions. Case studies of the management of fossils found in Fossil Cycad National Monument, the John Day fossil beds, the Charles M. Russell National Wildlife Refuge and surrounding areas of public land, the American Falls Reservoir, and Grand Staircase–Escalante National Monument are outlined. These examples provide a sense of the scope of fossils on federal public land, highlight how their management can be a challenge, and show that public land is vital for continued scientific collection and research.

ABSTRACT Along with the origin of life, the quest for the ultimate cause of the end of the dinosaurs and ~72% of other species is one of the most publicized questions in the history of our planet. So, it probably should not have come as a surprise that when Walter Alvarez and his team launched the impact-extinction theory, the opposition and the resistance against the theory was strong from the beginning and continues up to the present day. This paper follows the winding road around the roadblocks that were set up against the theory and how both the opposition against and accumulation of new data, e.g., the finding of the Chicxulub impact structure and extraterrestrial Cr isotope ratios to further develop the theory, went hand in hand. Often the roadblocks were overcome, but new ones were set up, and in the struggle to surmount these, the proponents were forced to look back on their arguments, to carefully re-formulate their viewpoints, and to check whether tunnel-vision had developed that might prevent seeing the data available in a different light. However, looking back on the competition among proponents and opponents 40 years later, the impact-extinction theory is stronger than ever before. It has survived and matured from a hypothesis into a well-established theory, although many questions remain to be solved.