2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 24
Presentation Time: 9:00 AM-6:00 PM


HELTON, Erica, Mendocino National Forest, USDA, 825 North Humboldt Ave, Willows, CA 95988, GYGLI, Samuel, Mendocino National Forest, USDA, 825 Humboldt Ave, Willows, CA 95988 and BELL, Angie, Klamath National Forest, 1312 Fairlane Road, Yreka, CA 96097, ehelton@fs.fed.us

Ultramafic rock (Um) may contain naturally occurring asbestos (NOA) which can pose a potential health risk when airborne. Published geologic mapping in the southern 1/3 of the Mendocino NF is at a reconnaissance level, making NOA risk assessment difficult for projects in this part of the Forest. This project will provide more precise mapping of Um bodies on the Mendocino NF and will be used to improve the NOA risk assessment and testing prioritization by mapping Um bodies in areas of high public use. Off-road vehicle use (OHV) is one of the primary public uses in this area. This project will also test the utility of air photo interpretation in delineating Um rock in the Lake Pillsbury area, and characterize the Franciscan rock units and their field relationships. Field review of the entire project area would be time consuming since the exact locations of the contacts are often hard to map due to dense brush and lack of outcrops. Air photo analysis, with some field verification, is a more efficient method for the identification and mapping of Um bodies over such a large area. This work will determine the extent to which this technique can be applied reliably on the Mendocino NF. The existing published and unpublished bedrock mapping was compiled. A field verification strategy, along with methods for note-taking, sample collection, and field photography were established. Field work was conducted through a field review of road cuts along trails and roads. The reliability of air photo interpretation was evaluated by designing field traverses to verify the presence or absence of Um rock as indicated by the air photos. Initial work suggests that air photo analysis is an efficient remote sensing tool for mapping Um rock on the Mendocino NF. GIS coverage of the Um bodies will be used to prioritize NOA testing and risk assessment. The mapping of Um bodies using air photos and field verification will be used to continually evaluate the reliability of the photos in allowing delineation of the bodies. Prioritization criteria for NOA testing on the Mendocino will be created by conducting GIS analyses to identify where bodies of Um rock coincide with areas of high use.