Paper No. 15
Presentation Time: 8:00 AM-12:00 PM
NATIONAL PARK SERVICE GEOLOGIC RESOURCE EVALUATION: GEOLOGIC MAPPING OF WALNUT CANYON NATIONAL MONUMENT AND PETRIFIED FOREST NATIONAL PARK, NORTHERN ARIZONA
A 210 km2
area comprising Walnut Canyon National Monument and the surrounding region in Coconino County, Arizona, was mapped in the Fall of 2002 as part of the National Park Service geologic resource evaluation program. The objectives of this mapping initiative were: 1) to characterize and document the geologic resources of the Monument; 2) to evaluate geologic hazards associated with Quaternary faults in the region; 3) and to test the utility of new GIS and handheld computer technology for geologic field mapping. Few geologic maps existed for this area; new mapping was carried out using a combination of traditional field tools and new technology utilizing hand-held tablet computers, high-resolution digital orthophotos, and integrated GPS. Although a number of faults in the Walnut Canyon area may have been active during Quaternary time, only the Anderson Mesa fault and the much smaller Marshall Lake fault display evidence of significant late Quaternary or Holocene activity. Activity on these faults poses a minor threat to Monument infrastructure and archaeological resources, primarily due to seismic shaking and rockfall hazards. Field GIS tools proved useful in low-relief and/or densely forested areas where terrain navigation is difficult. These tools also allow creation of geo-referenced map features while in the field, eliminating the need for digitizing. However, the clumsiness of the user interface led to significant lab time for cleaning and completing polygons. In some cases, traditional field methods, followed by digitizing, were a more efficient approach. It is anticipated that the next generation of digital mapping tools will create a more efficient and accurate interface between the user and the GIS.
Mapping of the southern half of Petrified Forest National Park is ongoing. A persistent problem facing researchers in Petrified Forest National Park is the lack of a regionally consistent stratigraphic nomenclature for the lower part of the Triassic Chinle Formation. Part of the purpose of this mapping initiative is to provide park personnel and visiting researchers a digital geologic reference map utilizing the most up-to-date locally defined nomenclature. Existing maps are field-checked and digitized, although many previously mapped units must be changed to match the recent stratigraphic nomenclature.