1

st 48 Project

Geology Report

February 5, 2018

Prepared by:

Natalie Cabrera

Acting Geologist

Six Rivers National Forest

Introduction

The Six Rivers National Forest Resource and Management Plan (Forest Plan) requires addressing the 

potential for increased mass movement for proposed timber harvest or building of roads and landings by 

development of landslide hazard maps and risk assessment (USDA 1995, p. IV-71). Unstable and 

potentially unstable lands (including earthflows) are included in Riparian Reserves as directed by the 

Aquatic Conservation Strategy (USDA 1995, p. IV-44, 45). They are defined as lands prone to mass 

failure under natural conditions and where human activities such as road building and harvest are likely to 

increase landslide distribution and frequency to the point likely to modify geomorphic and hydrologic 

processes. They include active landslides and those which exhibit sound evidence of movement in the 

past 400 years, inner gorges, and lands identified as unstable by geologic investigations (USDA 1994). 

The Forest Plan also requires compliance with federal regulations for airborne asbestos (USDA 1995, p. 

IV-116).

Geologic Setting

Bedrock

Lithologies include sedimentary, metasedimentary, and metavolcanics rocks. The Yolla Bolly terrane is 

comprised primarily of metagraywacke, with minor chert or meta chert, and mélange to broken formation 

of greenschist, blue schist, and chert. The Pickett Peak terrane is comprised predominantly of 

metagraywacke of the Valentine Springs Formation, and quartz-mica schist of the South Fork Mountain 

Schist with minor metabasalt, meta volcanics. 

Geomorphology

Landscape scale earthflows are mapped (McLaughlin 2000) at the lower mid-slope elevations along the 

west facing slopes of the Mad River canyon. One of these is in the project area and occupies units 613 

and 614. The mélange is the lower part of the earthflow in units 613 and 614. Other earthflows likely are 

included within Riparian Reserves around units 418, 419, 412, and 413. Shallow landslides were mapped 

in the field in units 603, 604, 403, 404, 401, and 306.

Caves 

The Federal Cave Resources Protection Act of 1988 (102 Stat. 4546; 16 U.S.C. 4301 et seq) provides that 

Federal lands be managed to protect and maintain, to the extent practical, significant caves. There are no 
known caves within the project area. No groundwater resources will be developed or are existing within 

the project area. 

Naturally occurring asbestos

Six Rivers National Forest has samples and tests for presence of Naturally Occurring Asbestos as close as 

10 miles from the project area. Two of the 42 samples within a 20 mile radius from the project area 

contained asbestos at 0.5% in small serpentenite outcrops. The project area contains no similar outcrops.

No ultramafic bedrock, and therefore no naturally occurring asbestos occur in the project area.

Unstable and Potentially Unstable Lands

The geologic effected environment consists of unstable lands that have potential to impact streams. The 

Six Rivers National Forest Resource and Management Plan (Forest Plan) requires addressing the potential 

for increased mass movement for proposed timber harvest or building of roads and landings by 

development of landslide hazard maps and risk assessment (USDA 1995, p. IV-71). Unstable and 

potentially unstable lands (including earthflows) are included in Riparian Reserves as directed by the 

Aquatic Conservation Strategy objectives which direct management activities to result in non-degradation 

and restoration of aquatic and riparian ecosystems. (USDA 1995, p. IV-44, 45). This is because landslides 

are a key component of the riparian system, supplying and metering sediment and large wood that are 

essential habitat elements of Pacific Northwestern river systems. Unstable lands are defined as lands 

prone to mass failure under natural conditions and where human activities such as road building and 

harvest are likely to increase landslide distribution and frequency to the point likely to modify 

geomorphic and hydrologic processes. They include active landslides and those which exhibit sound 

evidence of movement in the past 400 years, inner gorges, and lands identified as unstable by geologic 

investigations (USDA 1994). 

In order to meet Aquatic Conservation Strategy objectives, vegetation management activities follow 

several sets of guidelines including Land and Resource Management Plan standards and guides, best 

management practices (BMPs, USDA 2010), and project design features. These guidelines are 

incorporated into project analyses and design, and provide a set of practices which, during project 

implementation allow for both accomplishment of project objectives, and maintenance and restoration of

riparian function and condition. Because of these prescriptive methods, vegetation management within all 

unstable lands meet Aquatic Conservation Strategy objectives as project activities do not accelerate mass 

movement above background rates. This is largely achieved by restricting mechanical vegetation 

management to outside of unstable lands. 

The Forest Plan also requires compliance with federal regulations for airborne asbestos (USDA 1995, p. 

IV-116). 

Eight active landslides were identified in the project area including two deep seated earthflows. 

No ultramafic bedrock, and therefore no naturally occurring asbestos occur in the project area. 

Further risk of landslide activity is by intense storms. This trigger is unpredictable. Though, on average,

10-15 year magnitude storms are the most likely to produce mass movement (Spittler 1989, Wondzell and 

King 2003), actual storm intensities that can trigger landslides depend on antecedent and subsurface 

infiltration conditions (Iverson 2000, Roering and Jackson 2009). However, a major mitigating factor in 

reducing the risk of landslide activity is the prevention of high intensity fire itself through the proposed 

actions of fuels reduction and prescribed burning (Levitan 2013, Rolof et. al. 2005). The low burn 

intensities and retention of trees associated with the proposed fuels treatments minimize the longer term 

risks associated with high intensity burns such as decreased infiltration from hydrophobicity, and loss of 
root strength with vegetation clearing (Iverson 2000, Roering and Jackson 2009, Wondzell and King 

2003, Ziemer 1981, de la Fuente et. al. 2002).

Cumulative Effects

A major mitigating factor in reducing the risks of accelerating landslide activity is the prevention of high 

intensity fire itself through the proposed actions of fuels reduction and prescribed burning (Levitan 2013, 

Rolof et. al. 2005). The low burn intensities and retention of trees associated with the proposed fuels 

treatments minimize the longer term risks associated with high intensity burns such as decreased 

infiltration from hydrophobicity, and loss of root strength with vegetation clearing (Iverson 2000, Roering 

and Jackson 2009, Wondzell and King 2003, Ziemer 1981, de la Fuente et. al. 2002).

While there are areas of concern where project effects, such as mechanical ground-based yarding, might 

have short-term deleterious effects, such as locally triggering slope instability if not performed according 

to appropriate design features, the consequences of no action might be more significant from a slope 

stability perspective. Notably, following the 2008 array of large fire complexes across the Klamath 

Mountains, reactivation of deep-seated landslides has been observed in a number of high severity burned 

areas (Mikulovsky et al, 2012). Common factors among these reactivations include stand-replacing (high 

or complete tree mortality) fire in late seral or old-growth stands, and deep-seated landslides (earthflows, 

block sides, rotational/translational complexes, etc.) on highly sheared or unconsolidated geologic types. 

In all documented Klamath Mountains cases in the 2012 paper, the geologic substrate was Rattlesnake 

Creek Terrane, frequently mélange, often serpentinized. In the Coast Ranges, Franciscan rock types that 

are also frequently mélanges were involved. These are both common bedrock types in the project area. 

Because the project area has been fire-excluded for a lengthy period, it is likely that wildfire in the area 

would spread rapidly and extensively, and would burn at high severity in areas that resemble those with 

the described re-activated landslides. It is reasonable to assume then, that treatments such as those 

proposed, if they prove effective at reducing fire risk, will provide safer access for firefighters to contain 

fire starts, reduce the overall pattern of high burn severity on the landscape, and be effective in helping 

maintain hillslope stability and landsliding rates within their range of historic variability, and meet the 

desired condition under the Land and Resource Management Plan. If standards and guidelines, BMPs, 

and project design features are followed, negative effects to slope stability should be minimal or absent as 

compared to the likelihood that extensive landslide reactivation would be in the event of stand-replacing 

fire across much of the landscape.

Project Design Features

None needed above Standards and Guides, BMPs, and projects designs. 

References

Bosch, J.M. and Hewlett, J.D., 1982. A review of catchment experiments to determine the effect of 

vegetation changes on water yield and evapotranspiration. J. Hydrol., 55: 3--23.

De la Fuente, J.; Elder, D.; Miller, A. 2002. Does deforestation influence the activity of deep-seated 

landslides? Observations from the flood of 1997 in the central Klamath Mountains, northern California. 

Geologic Society of America 98th Annual Meeting Poster.

Iverson, R. M. 2000. Landslide triggering by rain infiltration. Water Resources Research, Vol. 36, No. 7, 

Pages 1897-1910. 
Levitan, F. 2014. Thoughts on high severity fire, deep - seated landslides, and fuels treatments in the Sims 

Fire restoration area. Six Rivers National Forest Sims Restoration project file. 1330 Bayshore Way, 

Eureka, CA 95501.

McLaughlin, R. J., Ellen, S. D., Blake, M. C., Jayko, A. S., Irwin, W. P., Aalto, K. R., Carver, G. A., and 

Clarke, S. H. 2000. Geology of the Cape Mendocino, Eureka, Garberville, and southwestern part of the 

Hayfork 30 x 60 minute quadrangles and adjacent offshore area, northern California. U. S. Geological 

Survey, Miscellaneous Field Studies Map MF-2336. Retrieved from https://pubs.usgs.gov/mf/2000/2336/

Mikulovsky et al, 2012. Reactivation of deep-seated landslides in northwestern California after wildfires 

in 2006 and 2008. American Geophysical Union, fall 2012 meeting, San Francisco, CA.

Reid, L. 2010. Chapter 6. Cumulative effects of fuel treatments on channel erosion and mass wasting. In 

Cumulative Watershed Effects of Fuel Management in the Western United States. USDA Forest Service 

RMRS-GTR-231-125.

Roering, J.J.; Jackson, M. 2009. Post-fire geomorphic response in steep, forested landscapes: Oregon 

Coast Range, USA. Quaternary Science Reviews 28, 1131–1146.

Roering, J.J.; Schmidt, K.M.; Stock, J.D.; Dietrich, W.E.; Montgomery, D.R. 2003. Shallow 

landsliding, root reinforcement, and the spatial distribution of trees in the Oregon Coast 

Range. Can. Geotech. J. 40: 237-253.

Rolof, G. J.; Mealey, S. P.; Clay, C.; Barry, J.; Yanish, C.; Neuenschwander, L. 2005. A process for 

modeling short- and long-term risk in the southern Oregon Cascades. Forest Ecology and Management 

211, 166–190.

Spittler, Thomas E. 1989. Controlled Burns on the Urban Fringe, Mount Tamalpais, Marin County, 

California. USDA Forest Service Gen. Tech. Rep. PSW-109: 43-48.

United States Department of Agriculture, Forest Service, Six Rivers National Forest. 1995. Six Rivers 

National Forest Land and Resource Management Plan. 1330 Bayshore Way, Eureka, CA 95501.

United States Department of Agriculture Forest Service. 2010. FS-990a: National Best Management 

Practices for Water Quality Management on National Forest System Lands.

United States Department of Agriculture, Forest Service, and Department of Interior, Bureau of Land 

Management. 1994. Final Supplemental Environmental Impact Statement on Management of Habitat for 

Late-Successional and Old-Growth Forest Related Species Within the Range of the Northern Spotted 

Owl, Volume I. 

Wondzell, S.M., King, J.G., 2003. Postfire erosional processes in the Pacific Northwest and Rocky 

Mountain regions. Forest Ecology and Management 178, 75–87.

Ziemer, R. 1981. The role of vegetation in the stability of forested slopes. Proceedings of the International 

Union of Forestry Research Organizations, XVII World Congress. Kyoto, Japan. Vol. I, pp 297-308. 
Analysis Framework: Statute, Regulation, LRMP, and Other Direction 

The following statutory authorities govern geologic resources and services activities essential to Forest 

Service programs:

Forest and Rangeland Renewable Resources Planning Act of August 17, 1974 (RPA) (88 Stat. 476; 16 

U.S.C. 1600-1614) as Amended by National Forest Management Act of October 22, 1976 (90 Stat. 2949; 

16 U.S.C. 1609). This act requires consideration of the geologic environment through the identification of 

hazardous conditions and the prevention of irreversible damages. The Secretary of Agriculture is required, 

in the development and maintenance of land management plans, to use a systematic interdisciplinary 

approach to achieve integrated consideration of physical, biological, economic, and other sciences. 

Federal Cave Resources Protection Act of 1988 (102 Stat. 4546; 16 U.S.C. 4301 et seq). This act 

provides that Federal lands be managed to protect and maintain, to the extent practical, significant caves. 

Asbestos Airborne Toxic Control Measure (ATCM) for Surface Application: The ATCM rule was 

adopted by the California Air Resource Board (CARB) in 1990 and amended in 2000. The amendment 

lowered the asbestos content to 0.25 percent for asbestos-bearing ultramafic rock materials used for 

surfacing applications subjected to vehicular, pedestrian or non-pedestrian use, such as cycling and 

horseback riding. In remote areas the naturally occurring asbestos (NOA) content can be as high as 1% 

without concern. 

Region 5 Regional Forester’s Direction on Naturally Occurring Asbestos issued February 11, 2009: 

The regional forester provided direction on addressing NOA on National Forest lands in California. “Any 

land management decisions regarding NOA must be based on sound data and analysis. According to EPA, 

the scientific assessment and identification of actual public health risks associated with NOA is a complex 

and time intensive process. Until such studies are performed, the Region will not have definitive 

information regarding actual employee and public health risks posed by NOA on national forest lands. 

Therefore, no decisions are being made or direction issued at this point in time to restrict or alter public 

access to and/or recreational use of the national forests.” The letter further directs forests to make the 

public aware of the potential risk of NOA and its presence on National Forest lands as well as guidance 

on how visitors can reduce their exposure to the substance.

Region 5 Regional Forester’s Naturally Occurring Asbestos Clarification on Interim Direction 

issued June 30, 2009:

The last sentence (as quoted above) is directed at public access or recreational use that is currently 

permitted on the forests. Any new proposed activities or projects on the forests that require NEPA would 

analyze NOA just like any other environmental hazard or concern. 

As an example, a forest would not add unauthorized trail segments to the travel management plan until 

analysis of the segment for NOA, water quality issues, fisheries or other issues of concern were analyzed.