Abstract Recent debris flow studies in Colorado indicate that the state is most susceptible to debris flows that initiate from surface-water runoff that erodes and entrains hillslope and channel sediment. These runoff-initiated debris flows grow in size by entraining sediment along travel paths, thereby increasing their destructive potential. Yet, the mechanics of initiation, erosion, and entrainment processes for runoff-initiated debris flows are poorly understood. The steep, bedrock-dominated flanks of the formerly glaciated Chalk Creek Valley near Nathrop, Colorado, generate an average of two runoff-initiated debris flows per year, making the valley an ideal natural laboratory for debris-flow research. This two-day field trip to the Chalk Creek Valley will examine debris-flow initiation areas, transport zones, deposits, and the impact of large pulses of debris-flow sediment on the morphology of Chalk Creek. On the first day, participants will hike into a particularly active basin at Chalk Cliffs where debris flows are being monitored by the U.S. Geological Survey, the University of Colorado, and East Carolina University. The second day will focus on debris-flow deposits in Chalk Creek and on recent debris flows in and near the community of Alpine in the central part of the valley.

Abstract The mineralogy of a leach cap over a subeconomic Mo-Cu porphyry deposit in the Grizzly Peak caldera in the central Colorado Rocky Mountains provides evidence of mineralization and indications of natural acid drainage potential. Airborne hyperspectral imaging (HSI) remote sensing is used to construct a spatially complete map of the leach-cap iron and clay minerals within the mineralized, acid-generating alteration zone. The mixtures of jarosite, goethite, and hematite provide direct indications of mineralization and acid source locations. The clay minerals illite (sericite), kaolinite, dickite, and pyrophyllite further characterize the alteration and appear to correlate with acid seeps. The illite chemistry is analyzed by mapping chemical substitutions of iron for aluminum and is highly correlated with acid sources. When integrated with mapped and interpreted structures, the controls on the acid drainage are revealed.

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 San Juan volcanic field comprises 25,000 km 2 of intermediate composition mid-Tertiary volcanic rocks and dacitic to rhyolitic calderas including the San Juan-Uncompahgre and La Garita caldera-forming super-volcanoes. The region is famous for the geological, ecological, hydrological, archeological, and climatological diversity. These characteristics supported ancestral Puebloan populations. The area is also important for its mineral wealth that once fueled local economic vitality. Today, mitigating and/or investigating the impacts of mining and establishing the region as a climate base station are the focuses of ongoing research. Studies include advanced water treatment, the acid neutralizing capacity (ANC) of propylitic bedrock for use in mine-lands cleanup, and the use of soil amendments including biochar from beetle-kill pines. Biochar aids soil productivity and revegetation by incorporation into soils to improve moisture retention, reduce erosion, and support the natural terrestrial carbon sequestration (NTS) potential of volcanic soils to help offset atmospheric CO 2 emissions. This field trip will examine the volcano-tectonic and cultural history of the San Juan volcanic field as well as its geologic structures, economic mineral deposits and impacts, recent mitigation measures, and associated climate research. Field trip stops will include a visit to (1) the Summitville Superfund site to explore quartz alunite-Au mineralization, and associated alteration and new water-quality mitigation strategies; (2) the historic Creede epithermal-polymetallic-vein district with remarkably preserved resurgent calderas, keystone-graben, and moat sediments; (3) the historic mining town of Silverton located in the nested San Juan-Silverton caldera complex that exhibits base-metal Au-Ag mineralization; and (4) the site of ANC and NTS studies. En route back to Denver, we will traverse Grand Mesa, a high NTS area with Neogene basalt-derived soils and will enjoy a soak in the geothermal waters of the Aspen anomaly at Glenwood Springs.

Abstract The Gold King mine water release that occurred on 5 August 2015 near the historical mining community of Silverton, Colorado, highlights the environmental legacy that abandoned mines have on the environment. During reclamation efforts, a breach of collapsed workings at the Gold King mine sent 3 million gallons of acidic and metal-rich mine water into the upper Animas River, a tributary to the Colorado River basin. The Gold King mine is located in the scenic, western San Juan Mountains, a region renowned for its volcano-tectonic and gold-silver-base metal mineralization history. Prior to mining, acidic drainage from hydrothermally altered areas was a major source of metals and acidity to streams, and it continues to be so. In addition to abandoned hard rock metal mines, uranium mine waste poses a long-term storage and immobilization challenge in this area. Uranium resources are mined in the Colorado Plateau, which borders the San Juan Mountains on the west. Uranium processing and repository sites along the Animas River near Durango, Colorado, are a prime example of how the legacy of mining must be managed for the health and well-being of future generations. The San Juan Mountains are part of a geoenvironmental nexus where geology, mining, agriculture, recreation, and community issues converge. This trip will explore the geology, mining, and mine cleanup history in which a community-driven, watershed-based stakeholder process is an integral part. Research tools and historical data useful for understanding complex watersheds impacted by natural sources of metals and acidity overprinted by mining will also be discussed.