SURFICIAL GEOLOGIC AND GEOLOGIC HAZARD MAPPING AT NEZ PERCE NATIONAL HISTORICAL PARK

Surficial geologic and geologic hazard mapping conducted at Nez Perce National Historical Park (NEPE) highlights the difficulties in balancing National Park Service needs and sensitivities of the Nez Perce people to land disturbances caused by standard on-ground geologic investigations. Balancing these differences was complicated because the wide spatial distribution and diverse geology of NEPE sites demanded intensive on-ground investigations.

The unique design of NEPE with 38 sites located in Idaho, Washington, Oregon, and Montana presented a logistical challenge when mapping because of the long travel distance between some sites. Diverse geology of the park made the mapping quite challenging. The geology mapped at park sites includes: Permo-Triassic Wallowa-Seven Devils Terrane that accreted to North America during the Cretaceous, Cretaceous extensional sedimentary basin-fill deposits, Miocene Columbia River Basalts and interbedded sedimentary deposits, Pleistocene Lakes Bonneville and Missoula Flood deposits, and glacial and periglacial deposits, and Holocene fluvial and alluvial deposits. Geologic and geomorphic features at several park sites are intimately linked to the history of the Nez Perce through oral histories about the origins of these features. Access on to some of the most sacred of these features was not permitted. Fortunately these features are small-scale (10’s meters) and float from the features could be examined to determine their composition.

Geologic hazards at NEPE sites were identified by on-ground investigation and interviews with people that live near the sites. Rock fall and slump to debris flow landslides hazards were mapped at two park sites. These landslides have and will continue to damage roads running through and near these sites.

The data collected in the field during the summer of 2001 and resulting maps were input into the NEPE Geographic Information System (GIS) database. The field data collected during the summer of 2002 and corresponding maps are in the process of being input into the same database. The NEPE GIS database will be used in the development of a resource management plan for the park. Descriptions of geologic units and the geologic histories of park sites developed while mapping at NEPE were used as the basis for a geology training session for the park’s staff.