Naturally Occurring Asbestos (NOA) deposits are most often found in ultramafic rock formations, often NOA is found in serpentine rock. Geologic maps prepared by the California Geologic Survey (formerly the California Division of Mines and Geology) show areas of higher probability for asbestos-containing rock within the broad zone of faults that follows the low foothills and lay in a south-east to north-west band. The Placer County communities of Auburn, Colfax, Meadow Vista, and Foresthill are among those that are within this fault band. Generally, the areas in Placer County that lay to the west of Folsom Lake and to the south of Wise Road are geologic areas that have a lower probability for the presence of NOA such as:
- Granite Bay
There are some isolated areas of higher probability for the presence of NOA within the Tahoe National Forest.
The identification of locations in Placer County that have the potential to contain NOA has been improved with the development of an enhanced 1:100,000 scale map by the California Geological Survey. This map denotes areas of Placer County that are more or less likely to contain NOA based on available soil and geologic studies, with some field verification. The enhanced map and accompanying report, Special Report 190, and information on how to purchase paper copies of the report are available at the California Geological Survey website. Enlarged maps have been prepared for different areas of Placer County where NOA may be found. These maps are available on the NOA Maps and Resources page.
The characterization of an area as having a lower overall probability of NOA presence means that although the likelihood is slight, in some instances NOA might be found within such an area. Similarly, locations in areas identified as being most likely to have NOA may not contain NOA.
NOA deposits have been found in rock other than ultramafic and serpentine rock; for example NOA deposits have been found in metavolcanic rocks such as the Copper Hill Volcanics in the Folsom vicinity. Metavolcanic rock formations are prevalent in areas to the northeast, north, and west of Auburn. Finally, in areas with sedimentary alluvial rock deposits such as those existing in western Placer County; it is possible that analytically detectable NOA may be found.