Abstract The Moscow-Pullman basin, located on the eastern margin of the Columbia River flood basalt province, consists of a subsurface mosaic of interlayered Miocene sediments and lava flows of the Imnaha, Grande Ronde, Wanapum, and Saddle Mountains Basalts of the Columbia River Basalt Group. This sequence is ~1800 ft (550 m) thick in the east around Moscow, Idaho, and exceeds 2300 ft (700 m) in the west at Pullman, Washington. Most flows entered from the west into a topographic low, partially surrounded by steep mountainous terrain. These flows caused a rapid rise in base level and deposition of immature sediments. This field guide focuses on the upper Grande Ronde Basalt, Wanapum Basalt, and sediments of the Latah Formation. Late Grande Ronde flows terminated midway into the basin to begin the formation of a topographic high that now separates a thick sediment wedge of the Vantage Member to the east of the high from a thin layer to the west. Disrupted by lava flows, streams were pushed from a west-flowing direction to a north-northwest orientation and drained the basin through a gap between steptoes toward Palouse, Washington. Emplacement of the Roza flow of the Wanapum Basalt against the western side of the topographic high was instrumental in this process, plugging west-flowing drainages and increasing deposition of Vantage sediments east of the high. The overlying basalt of Lolo covered both the Roza flow and Vantage sediments, blocking all drainages, and was in turn covered by sediments interlayered with local Saddle Mountains Basalt flows. Reestablishment of west-flowing drainages has been slow. The uppermost Grande Ronde, the Vantage, and the Wanapum contain what is known as the upper aquifer. The water supply is controlled, in part, by thickness, composition, and distribution of the Vantage sediments. A buried channel of the Vantage likely connects the upper aquifer to Palouse, Washington, outside the basin. This field guide locates outcrops; relates them to stratigraphic well data; outlines paleogeographic basin evolution from late Grande Ronde to the present time; and notes structures, basin margin differences, and features that influence upper aquifer water supply.

ABSTRACT Sedimentary rocks, ranging in age from Pennsylvanian to Cretaceous, crop out in the vicinity of the Dakota hogback. The rocks overlie Precambrian igneous and metamorphic rocks. The strata were deformed in late Cretaceous and early Tertiary time and dip to the east. Downcutting occurred in the Tertiary and Quaternary, formed the major canyons, and was interrupted by intervals of alluvial deposition east of the range front. Landslides mantle the east front of the hogback.

Abstract In 1901, Charles Van Hise asked Samuel Emmons and Whitman Cross to organize a grand excursion across Colorado as part of the combined meeting of the American Association for the Advancement of Science, GSA, and the Colorado Scientific Society (CSS). This trip replays part of that 10-day excursion across Colorado. Shortened to three days, this trip takes in some of the same sites as the 1901 trip, plus adds others of interest along the route where CSS members are reinventing geological interpretations. The trip will follow the precedent set in 1901; CSS members will serve as “site or stop hosts” in addition to the trip leader and drivers. While walking in the steps of the most famous of our profession we will also see some of the most magnificent scenery of Colorado.

Abstract The Boulder Creek Watershed, within the Front Range region of Colorado, istypical of many western watersheds because it is composed of a high-gradient upperreach mostly fed by snowmelt, a substantial change in gradient at the range front, andan urban corridor within the lower gradient section. A stream ecosystem within anurban landscape not only can provide water for municipal, industrial, and agriculturalneeds, but also can be utilized for recreation, esthetic enjoyment, and wastewaterdisposal. The purpose of this 26 km bicycle field trip is to explore the hydrology andgeochemistry of Boulder and South Boulder Creeks and to discuss topics includingflood frequency and hazards, aqueous geochemistry of the watershed, and potentialimpacts of invasive species and emerging contaminants on stream ecology. Keywords: Colorado Front Range, flood hazard, water quality, invasive species