Document xzJ07qD4j1Zwp7G426onjB676

New Idria Serpentinite: A Land Management Dilemma R.G. COLEMAN Department of Geological and Environmental Sciences. Stanford Umversiry. Stanford. CA 94305-2115 ________________ PLAINTIFF'S EXHIBIT SA-427 ENVIRONMENTAL & ENGINEERING GEOSCIENCE VOL. II, No. I, Spring 1966, pp. 9-22 EXHIBIT UCAREF00024240 Sew Idria Serpentinite: A Land Management Dilemma R.G. COLEMAN Department of Geological and Environmental Sciences. Stanford University. Stanford. C4 9J305-2II5 ABSTRACT The New Idria asbestos-bearingserpentinite rep resents a unique tectonic situation. Change in plate motion produced transverse compression across the San Andreas transform fault system in the vicinity of New Idria which produced shortening of the for mer continental margin resulting in sub-parallel thrusting, folding, and diapirisra. This tectonic acti vity has exposed a huge body of serpentinized mantle peridotite (45 sq mi) that may have been part of the Pacific Ocean crust basement Continued wedging of these peridotites into the water-rich continental crust has caused a chain-reaction serpentinization and expansion. Thousands oftectonic (milling) events acting on the serpentinite near New Idria created a huge deposit of short-fiber asbestos. The main ser pentine mineral is chrysotile that forms very short fibers (-5 microns) having a specific surface area 3 to 4 times greater than other commercial asbestos fibers. Its natural chemical solubility reduces its biopersistence resulting in much lower toxicity' to humans. During the last 15 million years the asbes tos-bearing serpentinite of the New Idria body has been eroded and contributes fibers to alluvial depos its along the west side of the San Joaquin Valley and San Benito River Basin with little to no indication of excessive present-day asbestos-related respira tory diseases in this area. A study by the Bureau of Land Management concerning exposure of asbestos fibers to weekend oEf-road vehicle riders in the New Idria serpentinite area indicates that their risk of developing lung cancer is low. Knowledge of the geologic facts concerning the natural origin and distribution of asbestos-bearing serpentinite illus trates the dilemma of the U. S. Government attempt ing to remediate the small EPA superfund mining sites within this vast region of serpentinite. INTRODUCTION There is a standingconflict between gavemmcntaeencies as to what management actions are required at the closed Atlas and Johns-Manville asbestos mines which '.he U. S. Environmental Protection Agency (EPA) has designated as superfund sites. These idle mine sites are within the New Idria serpentinite body and surround ing Bureau of Land Management (BLM) Clear Creek Management Area (CCMA) (Figure 1). Recreational value of this area is particularly high for off-road ve hicles (ORV) and oiher ORV activities. The purported dangers of inhaling asbestos-fibers has not gone unno ticed by the BLM. The BLM has developed a resource management plan to address the asbestos issue (Hastey. 1994). The BLM environmental impact statement at tempts to discuss the problems of multiple use. mining, ecology and EPA's jurisdiction of the superfund sties located on private land within the CCMA (Figure 1). The BLM resource management plan includes input from outside contractors, BLM personnel, and local citi zens and representatives of ORV clubs who use the area. BLM proposes six alternative plans for management of the Clear Creek Area which are now being considered (Hastey. (994). There are basic differences concerning the use of CCMA land due to perceived human-health risks from inhaling asbestos fibers made airborne by ORV climb ing on the soft serpentinite hills (Cooper et al,, 1979; PopendorfandWenk, !983;andRoss. 1994).ORV causes accelerated erosion of the soft serpentinite and contrib utes to more rapid erosion of the asbestos laden ser pentinite into the local streams. EPA has a mandate to ensure the protection of public health and the environ ment from "asbestos waste." The BLM is responsible for the balanced management of public lands based on the principles of multiple-use and sustained yield. The thrust of this paper is to illustrate that the as bestos-bearing serpentinite formed in a very unique tec tonic environment and is related to a change in plate motion along the San Andreas fault. The tectonic expo sure of this serpentinite was followed by 15 million years of denudation and dispersal of the asbestos which pre-dates asbestos mining and recreational activities. HISTORICAL ASPECTS OF MINING ACTIVITIES The New Idria area is one of the oldest and best known mercury mining districts in California with more than 60,000 flasks of mercury produced since the ori ginal discovery in IS58 (Eckel and Myers. 1946). Toxic mercury pollution in the stream waters draining into Silver Creek obliged the closing of this mercury mining Environmental < Engineering Geoscience. V'oI. II. No I, Spring 1996. pp. 9-22 9 UCAREF00024241 Coleman figure I. Clear Creek Management Area from BLM resource management plan and environmental impact statement (Hastey, 1994). district in the 1970s (Boctor et al.. 1987). Asbestos mining was originally only a small operation during the period from 1917 to 1920 which failed to prosper be cause high grade long fiber ore was not found and there was little demand for the short fiber ore from New Idria tWoolsey, 1922). This large deposit of short fiber as bestos was later '`discovered" by geologists in the late i950s. The short fiber asbestos could be easily milled and made available more cheaply to new markets in the Western United States such that a rush on the leasing of asbestos claims occurred in 1958 and 1959 (Bright, 1965). Union Carbide initiated its exploration program in 1959. The following year, Johns-Manville Corpora tion developed a joint venture with Kern County Land Company to form Coaiinga Asbestos Company (Mer ritt, 1962: Munro and Reim, 1962; and Rice, 1963). Coaiinga Asbestos Company constructed a plant site in Pine Canyon in :he headwaters of White Creek on a stabilized Holocene serpentinite debris flow. Initial asbestos production was 12,000-15.000 tons/yr. In 1961, Hidden Splendor Mining Company, presently known as the Atlas Minerals Company, acquired ad jacent properties in the spring of 1961 and began opera ting a plant situated on the higher levels of the White Creek serpentinite debris flow which had a production capacity similar to that in Pine Canyon. Union Carbide also began mining operations in 1961, but constructed an ore processing mill near King City 55 mi west of their mine. The Union Carbide operation using a wet milling process to purify the asbestos ore trucked from their Joe 5 open pit mine (Merritt, 1962). In 1985, the Union Carbide operation was sold to its employees and is now called King City Asbestos Corporation (KCAC). KCAC produces a trade product called Calidria Asbes tos. Through the research of Union Carbide scientists, it was established that Calidra Asbestos had unique char acteristics that could be used in numerous manufac tured products such as floor tiles, pipe, siding, and roof ing material (Mumpton and Thompson, 1975). The very pure New Idria asbestos could also be used for paper and a filler in adhesives and resins. In the mid 1970s these three mining and milling operations produced .0 Environmental < Engineering Geoscience. Vol. II. No l. Spring 1996. pp. 9-22 UCAREF00024242 New Idna Serpenumte '5.000 ions of asbestos tripling the production of Grade-7 asbestos in the United States at that time. The Johns-Manville (J-M) and Atlas mines were shut down in 1974 and 1979 respectively because of decreasing sales and increasing costs related to Federal Regulation. KCAC still operates the Joe 5 open pit mine supplying about 15.000 tons/yr of asbestos to the wet mill in King City. A conference held at New York Academy of Sci ences in 1964 discussed in great detail the biological affects of fibers in the lungs of asbestos workers reveal ing a "widening spectrum of asbestos malignancy" (New York Academy of Science. 1979). Thus, began a decade of intense medical research to establish the relationship between inhaling asbestos fibers and cancer of the lung or other organs. The Clean Air Act instituted in the early 1970s required that the Environmental Protection Agency (EPA) set national emission standards for hazardous air pollutants including asbestos. The Occupational Safety and Health Administration (OSHA) published rules in 1972 that were designed to protect employees working with asbestos. Mining operations are actually regulated by the Mine Safety and Health Administration (MSHA), whose rules are less restrictive than OSHA. Health ef fects of asbestos libers in animal experiments were ex trapolated to low doses causing fear of the carcinogenic aspects of asbestos fibers in schools or in natural settings such as the OR.V use in New Idria serpentinite area. A National Academy of Science report (National Acad emy of Science. 1984) on non-occupational health risks of asbestiform fibers was endorsed by some in the medi cal research community thereby supporting the conclu sion that there could be a correlation between inhaling low levels of asbestos fibers and cancer. This led to the notion that a "single fiber could kill" such as in the ambient air of offices and school buildings (Selikoflf and Lee, 1979). Using the National Academy of Science report (National Academy of Science, 1984) as their guideline OSHA and EPA (Asbestos Hazard Emergency Response Act of 1987) issued regulations pointing out that asbestos fibers can be a potent carcinogen. Therefore OSHA and EPA set the maximum work place exposure of asbestos fibers at 0.1 fiber per cubic centimeter over an 3 hour work day. Environmental sampling for asbestos was instituted nationwide. In 1980. EPA regulators discovered asbes tos fibers m water and stream sediments in Arroyo Pasajero, which were further traced up-stream along Los Gatos Creek and its tributary White Creek. White Creek drains ihe southern part of the New Idria serpentinite body where the J-M and Atlas asbestos operations were located (Figures l and 2). Elevated levels of asbestos were also detected in water samples from the California Aqueauc: System near Los Angeles. Additional studies of the asbestos fibers in these waters by EPA, U.S. Bureau of Reclamation, and California Department of Water Resources pinpointed the source of the fibers as coming from the Arroyo Pasajero Ponding Basin loca ted just west of the California Aqueduct, near Huron, a small town east of Coalinga (Figure 2). A similar re port (Kanarek et ai., 1980) on asbestos and epidemio logical incidence in drinking water of the San Francisco Bay area created further concern by health officials. By 1983 these studies led to placing the idle Atlas and J-M asbestos mines on the Superfund National Prionties List as some of the nation's most serious hazard ous waste sites. Tn 1991. EPA's regional Administrator signed documents defining the methods EPA planned to use to cleanup these two sites. In the meantime, KCAC suit operates the Joe 5 open pit mine in compliance of regulations established by the Mine Safety and Health Administration (MSHA) and EPA. KCAC's commercial asbestos product is pri marily exported overseas, as the market for asbestos has continued to decline in the United States. However, with a 1991 court overturn of EPA's 1989 Asbestos Ban and Phaseout Rule of most asbestos-containing products, me decline in U. S. asbestos consumption appears to have leveled off at about 28.000 metric tons (Skinner and Ross. 1994) The fact that the New Idria asbestos-bearing serpenunite body is not just confined to White Creek drainage area (Figures l and 2) and contains 20-30 volume per cent of asbestos fibers in all of its natural exposures appears to have been overlooked when the superfund sites were selected. The New Idria serpentinite is pres ently being eroded by ail of the streams draining it. Asbestos bearing layers are present within older terrace deposits along streams draining the New Idria serpen tinite body. These asbestos layers provide a Holocene stratigraphic history of asbestos transport onto the al luvial fans of the San Joaquin Valley. Examination ot stream terraces along the Los Gatos Creek a few miies east of Coalinga reveal that asbestos-bearing layers con tain charcoal derived from transported wood fragments that give a C1* age of 500 B. P. (Atwater et al., 1990). The anthropogenic disturbance of the New Idria serpentinite body by mining and recreation pales :n comparison to the naturally occurring, and continuing erosion of asbestos-bearing clastic debris throughout the Holocene (Coleman, 1986). The following sections will develop the relationship beeween geologic evolu tion, tectonism, nature of the asbestos-bearing serpen tinite, and its continuing erosion. GEOLOGIC EVOLUTION OF SERPENTINITE Tne New Idria serpentinite body forms the core of an elongate antiform that lies between the San Andreas fault on the west and the San Joaquin alluvial valley Environmental &. Engineering Geoscience. Vol. .'(. So. !. Spring 1996. pp. 9-27 UCAREF00024243 Coleman Figure l. Geomorphology of the area surrounding the New [dri* serpenunite miss. on the east. Tertiary and Mesozoic sedimentary rocks surrounding the serpentinite body are folded and thnist into a senes of anticlines and synclines whose etteckelon foid axes form acute angles with the northwest trending San Andreas Fault (Dibblee, 1971; Nilsen and Dibblee, 1979; Figures 3 and 4-). The serpentinite body is in contact with the Franciscan subduction assem blages of Jurassic-Cretaceous age and the Upper Cre taceous Panochc and Moreno formations of the Great Valley forearc sedimentary sequences of marine sand stone and shale (Coleman, 1986). The basement for the west side of the Great Valley sequence is considered to be ophilites that formed as pan of an intra-oceanic arc in Late Jurassic (169-161 ma; Hopson et a!., 1981; Robertson. 1989). Tertiary marine sediments, as young as Pliocene, unconformably overlie the Franciscan sub duction complex and the Great Valley sequence (Diboiee, 1971; Nilsen and Dibblee, 1979; and Graham et a!., 1989). The contact of the serpentinite body with :he surrounding sediments is marked by zones of dis location that record upward tectonic movement (Cole man, 1980). The northeastern contact along the New Sdria serpentinite has been called a thrust as the subacent Mesozoic and Tertiary sediments are overturned by emplacement of the expanding serpentinite protru sion (Eckel and Myers, 1946; Coleman, 1957; Figure 3) Synthesis of the geophysical data gathered by the USGS from the 1983 Coalinga earthquake and the Pirkfteld study produced an explanation for these basement structures (Rymer and Ellsworth, 1990; Wentworth et al., 1992), The surface expression of westward thrust ing seen in seismic profiles is thought to be related to eastward thrusting of a tectonic wedge of the Francis can subduction complex consisting of trench sediments and oceanic crust (ophiolites), as shown by (Wentworth and Zoback. 1989, 1990). Geophysical measurements cannot distinguish between Great Valley or Franciscan ophiolites or younger and deeper ocean crust from the Pacific plate, and so. published reconstructions usually show the basement beneath the Coalinga antiform as a continuous monolithoiogic amt consisting of Great Valley basement (ophioiite) (Gnscom and iachcns. 1990; Namson et al., 1990; Waiter, 1990; and Wcntwortn and Zoback, 1990). The compressionai regime between the San An dreas fault and the Great Valley fore-arc sequence pro duced eastward wedging of the stranded Franciscan package of trench deposits and underlying oceanic crust Environmental & Engineering Geoscience. Vol. II. No. I. Spring ;996, po 9--Z2 UCAREFG0C New Idru Serpciuimic UCAREF00024245 Coleman San Andreas Waunam Canyon -aun Gnswaia Hiiis \un Tp 't''<3v M( <-(?^uCHS ^eakV^ ec-ios Turney Hills Sw , San joacum Vailey Mf cm _1 O Scale T. 5 cs .V.lanne r * * * if*/*' * '* " Great Valley Basement I lO km ------------------ E. O ^ Waanam Canyon Fault New iana seipantimte 'o White Creek Synctme f Tp 9] Slue A.' Tp Wa.ltham Can7yon FauK 'P / Coaknga Anticline r J, oaquin Fntnjga White Creek Syndtne B<g Blue 4-6.5 km/sec O c- Figure 4. Geologic cross sections. See Figure 3 far locations and explanation of rock units. Venice! scale l/l horizontal. (Wentworth et al.. 1984.). Detached and stranded slabs of oceanic crust consist of large volumes of peridotite which became serpenunized by water pumped into the new compressional regime caused by change in plate motions (Page and Brocher. 1993). Accelerated water pumping into the peridotite as it wedged into the lower crust increased production of serpenlinite accompanied oy incremental volume increase greater than 15 percent .n local areas (Coleman and Keith. 1971). A concomi tant decrease in density accompanies serpencinization enabling an upward buoyancy effect on the serpentinue which is surrounded by more dense country rock. The lighter and Theologically weaker serpentiniie can move upward and laterally lubricate the west-directed biind thrust fault zones (rrwin, 1977; Coleman, 1980: Figure 4). The firs: breaching of the New Idria serpentinite body :n Early or Middle Miocene is marked by asbestos bearing serpentinue clastic debris in the Big Blue For mation of Miocene age derived from the tectonically exposed serpentinue (Casey and Dickinson. 1976: D.ckinson and Casey. 1976; Carlson. 1984; and Bate. 1984; Figure 5). It is estimated that 15 tmJ of debris mass wasted or was eroded during this early unroofing (Figures 3, 4, and 5). This initial spectacular serpenti nite protrusion (Lockwood. 1971) was followed by a continuous record of serpentinite (asbestos-bearing) deposition in the San Joaquin 3asin and Vallecitos synfocm (Graham. 1995). The record of serpentinite ero sion is verified by the presence of detrital serpenttnue flakes in the Etchegoin sediments (5 ma), San Joaquin Formation (3 ma) and Tulare Formation (2 ma). The presence of active iandslidcs on the flanks of the New (dria serpenunite body (Cowan and Mansfield. 1979) and the deposition of detrital serpentinite in terrace de posits as young as 500 B ?. (Atwater et al., 1990) is strong evidence that the New Idria serpentinite mass continues to move tectonically upward and will do so as long as the compressive regime prevails and sub surface serpencinization of Franciscan opniolite mantle continues. USGS (Wentworth et al.. 1992) studies show that blind thrusting during the Coalinga earthquake under the crest of the Coalinga anticline along Los Gatos Creek resulted in more than one meter of uplift. Integrating periodicity of earthquakes over a longer time period and estimating repeat times 1200-1.000 yr) for similar in tensity earthauakes gives an uplift rate of 1-2 mm/yr Environmental & Engineennf Geoscience. Vol. II. No 1. Spring 1996. ?p 9-21 UCAREF00C2424 New Idria Serpentimic Coast Ranges San Joaquin Basin CD Oetr&ta/ asdesrcs-beanrig serpentinite deposition, diagrammatic. Figure 5. Sequence stratigraphy for the New Idria serpeminiie and its surroundings. (Stein and King. L9S4-; Atwater et ai.. 1990). Assuming the repeat times for seismic events (200-100 yrs) have remained constant for the last 20 ma. the region could have undergone more than 20,000 to 100.000 seismic events related to continued thrusting and uplift of the area (Stein and King. 1984; Atwater et al.. 1990) Each of these seismic events would introduce more water into the system sustaining serpentinization and expansion (Coleman, 1971; Coleman and Jove, 1993). The long term deformation of the serpentinized peridotite leads to tectonizacion and milling. The exposed asbestosbeanng serpentinite represents the final product of this '`tectonic milling" (Mumpton and Thompson, 1975). NEW rDRIA SERPENTINITE BODY Serpentinues generally are derived from ukntmafic rocks that make up the Earth's upper mantle, past plate tectonic movements have accreted large masses of man;;e peridotite and us serpentinized equivalents within the active subduction zones of the western North American continental margin. The instability of perido tite in (he presence of water at crustal temperatures leads to its continuing hydrothermal alteration forming asbes tos veins or disseminations within the serpentinized pendotite in the Earth's crust (Coleman and Jove, 1993). The New Idria serpentinite body contains mamly highly sheared aid crushed incoherent material that is made of soft, crumbly aggregates, and sheets of asbes tos material (Mumpton and Thompson, 1975). The ser pentinite has little strength at the surface, and the landforms which develop on it are rounded hills and easily eroded. The flanking landslide masses are derived from the rising unstable serpentinite body (Cowan and Mans field, 1979; Figure 6). . The unique aspect of the New Idria serpentinite is that the original mantle peridotite has been completely altered. It contains up to 60 percent asbestos associated with lizardite. bmcite, and magnetite with only a few rare scraps of primary mantle peridotite procoltth con sisting of olivine, pyroxene, and chromite. These few scraps of preserved peridotite contain original mantle mineral assemblages typical of depleted harzburgites commonly present in some of the less serpentinized peridotites of the California Coast Ranges (Loney et al., 1971). From the authors petrologic studies (Coleman. 1971, 1980) of California peridotites, harzburgite is the main mantle protolith with smaller amounts of dunite. Only rarely is clinopyroxene present, explaining the low silica activity during the main phases of serpentinization. The reddish-brown ribs of silica carbonate rock within the New Idria serpentinite body developed during a very late regional hydrothermal event which produced the mercury deposits. .As described above, the repeated tectonic activity related to compression has facilitated extreme shearing and pulverization of the setpentiniie. The important min erals formed during serpentinization are chrysotile (asbestos), lizardite. brucite, and magnetite. Mineralogic studies of the New Idria serpentinite show that chrysotile is the predominant constituent (50-75 per cent) in the asbestos ore samples (Mumpton and Thomp son, 1975). Brucite content may be as high as 10 percent, more than double expected in other chrysotile asbestos deposits. Talc is only rarely reported and its absence indicates the very low activity of silica during serpentinization. The sheared and pulverized serpentinite is made up of flexible light greenish colored flakes re sembling leather. The larger fragments may have ker nels of massive green unsheared serpentinite consisting of lizardite with minor chrysotile. The outer surfaces of these larger pods of coherent massive serpentinite are completely sheeted and plated with the flexible leather like chrysotile (asbestos), which retain slickenside marks of their tectonic transport. The widespread occurrence of brucite (Hostetler et al., 1966) and its destruction in the weathering zone produces Mg-HCO: waters Environmental Jt Engineering Geoscience. Vol. II. No. 1. Spring 1996. pp. 9-22 UCAREF00024247 Coleman Oibblee (1971). Estimation of landslide area only approximate. (Mumpton and Thompson, 1966). Within the weathering zone hydromagnesite, artinite, coalingite, and pyroaurite are produced by bnicitc dissolution and are pre cipitated from Mg-HCOj waters during the dry season (Barnes ct al., 1967). At deeper levels the Mg-HCOj waters loses bicarbonate promoting precipitation of secondary chrysotile (asbestos) (Mumpton and Thomp son, 1975). The formation of asbestos in New Idria is unusual since most asbestos deposits contain mainly cross-fiber asbestos veins (1 to 1/16 in. thick) which make up 10 to 20 percent of the serpentinite. In contrast, 50-70 per cent of the serpentinite exposed at the surface of the New Idria serpentinite consists of sheared and flatxned material that is soft, and powdery chrysotile (as bestos) within the sheared leathery flakes or agglom erates. The incompetent mass of chrysotile is easily eroded and is present as clastic debris in all the major streams draining the New Idria body. This rapid erosion of the serpentinite body has inhibited the formation of soil;- on most of its surface. The present drainage pattern reveals that transportation of asbestos fibers by natural erosion is widespread and not confined to the south end of the body (Figure 2). NATURE OF THE ASBESTOS FIBERS Chrysotile is the main asbestos mineral present in these asbestos bearing deposits but is oftea associated with lizardite and antigorite which are non-fibrous forms of the serpentine mineral group (Skinner and Ross. 1988). Electron microscope studies on the New Idria material show that the fiber lengths are variable with an average length of 5 microns. The longer fibers are present in the leathery sheets and flexible platelets (Mumpton and Thompson, 1975). Physical data on the New Idria as bestos fibers (Mumpton and Thompson, 1975) are: 1. Diameter: 260-129 A average with a narrow size distribution. 2. Length: 5 microns average range 1-20 microns. 3. Surface area: 60-70 m:/g. Environmental & Engineering Geoscience. Vol. It. No. 1. Spring 1996, pp. 9-22 UCAREF00024248 New Idru Serpentimie X-ray diffraction studies of the New Idria chrysottle show that it consists of a brucite-like layer with oc tahedral coordination of its cations coupled to tridymitelike layer of silicate tetrahedra and curled into a hollow cylinder typical of normal chrysottle fibers (Mumpton and Thompson, 1975: Campbell et al, 1978; and Wicks and O'Hanley, 1988). It is important to note that no amphibole asbestos has been reported in any of the mineralogical studies made of the New Idria asbestos deposits. A very minor amount of tremolite is present along the boundaries of some of the tectonic inclusions wtthtn the New Idria serpentinite. Epidemiological stu dies show that chrysottle asbestos free of amphibole fibers are not be linked to mesothelioma (McDonald and McDonald. 1995) The significant features of the New Idria asbestos fibers is that they are very short, have a small diameter thereby reducing its cohesive properties, and have a specific surface area that is 3 to 4 times as great as other commercial short fiber chrysolite (Mumpton and Thompson. 1975). Easily respirable chrysotile fibers have the potential for deep penetration into human lung tissue, however the very fine nature and high surface area leads to a low bio-persistence rate. The low biopersistcnce rate is related to its natural chemical solu bility which is greater than most other chrysotile or am phibole fibers of similar length. Epidemiological evi dence concerning the toxicity of the New Idria asbestos is scarce. An employee medical surveillance program in effect since 1963 by Union Carbide and KCAC.of its employees involves a cohort of about 450 workers-- 40 of whom have been employed for over 15 years. The Southern Monterey County Medical Group and other physicians have not detected asbestos-related ra diological changes, shortness of breath, or rales (asbestosis) in this cohort. Detailed autopsies on two deceased members of this cohort who had worked with asbestos over 25 years revealed no asbestos-related disease (ICCAC Inc.. 1995). EROSION OF THE SERPENTINITE BODY The Now Idria asbestos-bearing serpentinite body occupies the highest elevations of the Joaquin Ridge (San Benito mountain 5,242 ft) forming mostly subdued surfaces within the outcrop of the serpentinite. The serpentinite body is surrounded by uplifted coherent sediments that form steep ridge and valley topography particularly along the northeastern flanks of the body. This high standing New Idria body is quite unusual considering how easily the New Idria serpentinite can ae eroded (Figure 2). The major drainage away from `.ne serpentinite body is radial and marks the uplift area of the serpentinite body. The main streams draining the area toward the San Joaquin Valley are Los Gatos Creek. Salt Creek. Cantua Creek. Arroyo Honda, and Silver Creek all of which contribute asbestos-bearing sedi ments to the western alluvial fans of the San Joaquin Valley (Figure 2). The headwaters of the San Benito River are located within (he serpentinite body and com bine with Clear Creek to form a drainage system which is regulated by the Hernandez Reservoir. The San Benito River joins the Pajaro River which then enters the Pa cific Ocean near Moss Landing within the Monterey Bay. All of these streams are intermittent and only dur ing the wet season are they active and free flowing (Figure 2). Those streams flowing into the San Joaquin Valley seep into the alluvium west of the California aqueduct but during flood stage sediments are introduced into the California aqueduct, as well as asbestos fibers from the New Idria serpentinite body. The streams draining the serpentinite area are actively eroding the body. The draining streams have V-shaped valleys particularly within the serpentinite area and around its flanks. An excep tion to the V-shape is the flat stream valley of the San Benito River as it flows northwesterly along the flanks of the serpentinite body. Well developed "mortar beds" (concrete-like gravels, cemented by carbonates) form during the dry season when evaporation of the super saturated water precipitates carbonates (Barnes et al., 1967). Once the "mortar beds'* form they are resistant to erosion and promote development of broad flat stream bottoms along the San Benito River within the serpen tinite body and in the Hernandez Valley along the northwestern flanks of the body. Considerable serpen tinite debris fasbestos-bearing) is locked in these car bonate cemented elastics, which are more resistant to erosion than the surrounding sediments. Perched ter races ofthese resistant "mortar beds" are preserved within the serpentinite body and in White Creek. Tne mortar beds mark the history of erosion and uplift of the serpentinite body. The presence of landslides along the flanks of the serpentinite body are of special interest as they dem onstrate large scale mass wasting of the serpentinite (Cowan and Mansfield. 1979). Twenty three Holocene landslides mapped on aerial photos have an estimated total volume of 17.60 x 109 m3. The debris slides de veloped within the serpentinite body are moving down ward into the headwater streams and pose a potential hazard during heavy rainfall or seismic events (Harp and Keefer. 1990; Brabb. 1991; Figure 6). The debris caught in the steep valleys characteristically cause development of double drainage patterns. Consequent post-slide erosion clears these choked stream valleys contributing serpentinite elastics (asbestos-bearing) dur ing the rainy seasons. The author has estimated that the White Creek landslide occupying much of the south western part of the serpentinite body contains 4.8 x 10 m3 of asbestos-bearing serpentinite (Figure 6). This huge debris slide contributes material directly to White Environmental Jc Engineering Geoscience. Vol. II. No. I. Soring 1996. pp. 9-22 UCAREF00024249 Coleman Creek which connects downstream with Los Gatos Creek, which in turn terminates within the large Arroya Pasajero alluvial fan on the west side of the San Joaquin Valley. The Arroyo Pasajero alluvial fan. a prominent feature on the west side of the San Joaquin Valley, consists of many layers of flood transported Holocene serpentinite clastic (asbestos-bearing) debris. The Cali fornia Aqueduct gently curves around the Pasajero allu vial fan at the 100-m contour interval and is definitely vulnerable to contamination and damage from seasonal floods carrying asbestos-bearing material from the Mew tdria serpentinite body (Figure 2). Alluvial fans at the termination of Cantua Creek and Silver Creek are similarly formed and also contain Holo cene asbestos-bearing debris in their flanking terraces (Figure 2). In March t995, a major storm produced an erosional scenario described above causing widespread flooding and deposition of asbestos-bearing debris upon these alluvial fans and in the San Benito River drainage system. The present drainage pattern developed on the ser pentinite body is inherited from earlier Holocene up lift and erosion. Woodward and Clyde (1989) and PTI (1993) estimate an erosion rate of 8 ydJ per acre or approximately 4.5 x 10-4 km/yr (4 mm/yr). Non-marine sediments containing serpentinite elastics (asbestos bearing) that rest on the northwest edge of the ser pentinite body (Rentschler, 1989) can be correlated with sediments within the Vallecitos synform (Figure 3). The youngest sediments are estimated to be 2-5 million years (Pliocene; Rentschler, 1989) and have a vertical dis placement of approximately 2,800 ft (853 m) from the trough of the Vallecitos syncline to the crest of ser pentinite body uplift. This vertical displacement can be used to estimate an uplift rate of 1.7 to 4 mm/year de pending on the age of the sediments. The estimated current rates of 4 mm/yr are in excess of usual erosional rates of 1-2 mm year for mouncainous areas and dem onstrate long-term, rapid erosion and tectonic uplift of the New Idria serpentinite body in comparison with the rest of the Coast Range (Harrison. 1994). Implications of these high erosion rates coupled with continued tec tonic uplift of the asbestos-bearing serpentinite body are significant and must be considered in light of any remedial action at the superfund sites. PUBLIC LAND USE California citizens' awareness of the management of public lands has produced a climate of conflict between the various users such as recreation, conservation, min ing, and grazing, and the potential for toxic hazards. The New Idria serpentinite body is situated within the BLM Clear Creek Management Area (CCMA) which encompasses approximately 50,000 acres (Figure l). Contained within the CCMA are approximately 9.600 acres of private land and 1.920 acres of California State Land. A large share of the private land within the CCMA is related to early mining claims. Some of the private land is used for cattle grazing. The BLM is responsible for a balanced management of these public lands based on multiple use and sustained yield. BLM claims to take into account the long-term needs of future generations related to the renewable and non-renewable resources (Hastey, 1994). As noted earlier, the EPA declared in 1983 (he Altlas and Coaiinga (Johns-Manville) areas as superfund sites which are within the CCMA (Figure I). These superfund sites encompass approximately 1,300 acres or about 4 percent of the caul exposed asbestos bearing serpentinite body. Another facet that requires regulation is the well known and unusual endemic vegetation within the ser pentinite area (Kruckcberg, 1984; Proctor et al,, 1993). A recent BLM study of the plant communities on the serpencinite produced a startling report that the San Benito evening primrose (Camissonia bertitensi) is now a threatened species and is listed by the U.S. Fish and Wildlife Service Endangered Species Act of 1973 (Tay lor. 1990). This discovery adds yet another aspect to the management of the CCMA, because the BLM is required by law to protect the habitat of endangered plant species on the serpentinite. Proposals are under way to include seven other species on the endangered list (Hastey, 1944). The BLM management decisions become even more difficult in light of the new legislative constraints in volving ORV use in CCMA. EPA requires the BLM to assess the risks of naturally occurring asbestos in the CCMA as had been done previously for the superfund sites at the asbestos mines. The ORV private groups are asking for common sense rulings concerning rec reation in this area. RISK ASSESSMENT OF SERPENTINITE AREAS The occupational hazards related to inhaling large amounts of amphibole asbestos fibers arc documented (Ross. 1993; Skinner and Ross. 1994; and McDonald and McDonald, 1995). A difficult problem remains in determining acceptable low-level exposures to the less dangerous chrysotile asbestos-bearing New Idria ser pentinite. A significant question remains concerning management of the New Idria: Is the risk too high for unknowing citizens to use the CCMA area for recrea tion or for raining activities? Such uncertainty remains because of a fundamental scientific disagreement con cerning the actual threshold risk (lowest safe limit of ftbers/cc) for inhalation of asbestos fibers (McDonald and McDonald. 1995). There is no consensus on what the safe threshold should be for asbestos fibers at low levels and with intermittent exposure (McDonald, 1985). IS Environmental & Engineering Geoscience. VoL II* No. 1. Spring 1996, pp. 9-23 UCAREF00024250 New [dria Serpeniinite An independent consultant was contracted by the 3LM to evaluate the risk to human health caused by exposure various activities within the CCMA (PTI, 1992). Their study focused on the risks associated with inhalation of asbestos while using an ORV, or while camping and hiking in the CCMA. Data utilized was from three separate sources: 1. EPA. 2. BLM health and safety program. 3. An earfier study at the University of California (Cooper et al,, 1979; Popendorf and Wenk, 1983). The risk calculations prepared by PTI appear to be arbi trary. The PTI report combined their new data with that from the three previously cited data bases above and from a combination these data developed a relationship between excess lifetime cancer risk and the chronic daily exposure as follows: Excess Lifetime Cancer Risk = EC x URF where: EC = Chronic daily exposure to asbestos in air averaged over an individual lifetime. URF = Unit risk factor for inhalation of asbestos (0.23 f/cc) (established by EPA from occupational studies on asbestos workers; PTI. 1992). Risk estimates on the mean concentrations exposure due to ORV and other site uses was derived from the PTI data for BLM which gives 0.066 to 0.04 f/cc. These values are based on actual measurements from personal monitors attached to ORV motorbike riders under vari ous conditions. Table l shows that these measured values yield risk levels between 2 x 10`* to 3 x 10"4 RME (reasonable maximum exposure). The acceptable risk levels cited by the U.S. National Contingency Plan for Superfund cites are between 10"4 and IQ-4, values higher Table !. Upper-bound lifetime excess cancer risk estimates asso ciated wuh activities at the Clear Creek Management Area (taken from PTI. 1992). Excess Cancer Risk at Exposure Levels* Exposure Scenarios 1-Dsy RME6 High Estimate OIT-Road Riding Other Activities (camping, hiking) Combined Activities 4x10** 2xl0*s lxl0~5 3x1 O'1 Ixl0-J 5x10-s 6x10*J _C 9xlO-J `Risk estimates are based on inhalation exposures only. 6RME: reasonable maximum exposure. The high estimate was derived from a site visitor's estimate ofsite use .'or off-toad vehicle riding. The RME estimate for other activities was combined wuh this estimate. than these are unacceptable. There are uncertainties in the BTI data set provided BLM when compared to ear lier estimates by Popendorf and Wenk (1983). but all of these values provide a initial preliminary estimate of exposure for this environmental setting. Because these esu'maied risks are borderline other independent mea surements should be made before final management decisions are made for CCMA. The BLM is concerned with the risk aspect versus the recreational value of the CCMA. A recently com pleted BLM study proposes six alternative plans taking into consideration the many factors discussed earlier (Hastey. 1994) [t is obvious that the remoteness of the New Idria serpentinite body and the ORV activity com bined with camping represent an important recrea tional resource. Excessive ORV use is not compatible with the environment and often can cause accelerated erosion in areas of intensive use (Webb and Wilshire. 1983). Studies continue to show that if exposures are only to chrysotile asbestos, even if the exposure is more than 10 times higher than that recommended by the EPA. such exposures result in no excess lung cancer in co horts monitored for periods up to 15 years (Weill et al., 1979; Thomas et al., 1982; Ohlson and Hogstedt, 1985; Churg. 1986; and Newhouse and Sullivan. 1989) Reports such as these indicate that inhalation of chryso tile asbestos fibers are dangerous only when doses ex ceed 10 f/cc; and such a dose is much higher than present OSHA recommended levels 0.1 f/cc. If these data are included in common sense risk analyses, it emerges that the immediate toxic aspects of the chrysotile asbestos for ORV enthusiasts and campers in New [dria is low. Using this information, one is forced to the conclusion that the perceived risk from the asbestos fibers in the New Idria area related to ORV activities actually amount to no more than a "phantom risk" (D'Agostino and Wilson. 1993). CONCLUSIONS The New Idria asbestos-bearing serpentmite body is a unique geologic phenomenon created by plate tectonic evolution of Western North America. Change in plate motion across the San Andreas fault system has produced shortening of the former continental margin which is manifested by sub-parallel thrusting and folding. Con tinued wedging of the peridotites into the continental crust developed a chain-reaction serpentinization ac companied by expansion. Tnousands of tectonic events acting on the serpentinite has produced a huge deposit of short-fiber asbestos by tectonic milling and recrystallizacion. Erosion of this tectonizcd serpentinite since Miocene (15 ma) has introduced asbestos-bearing clastic material into all of the sediments deposited along the Hanks of the serpentinite body. The present configuration Ejivinmmcntal En^inccri/ig Cff'u :ctcc. Yul. II. No. :. Sprint! 1996. pp. 9-22 19 UCAREF00024251 Coleman and drainage patterns around the serpentimte mass show stratigraphic evidence from their associated stream ter races that Holocene deposition of asbestos-bearing serpentimte has been continuous and pervasive up to the present time (Figure 5). Careful geologic, ecological, and land-use studies should always be made at waste sites so that the role cf nature is understood and can be utilized for common serse remediation. The initial studies of any superfund sue should also seek the input of local citizens or in dustry. wno often retain important historical records of their land use. ACKNOWLEDGMENTS The views presented in this paper represent those of the author and are not beholden to any vested interest either commercial, governmental, or academic. This study was supported by the author's personal funds and nominal services provided emeritus professors at Stan ford. I would like to acknowledge reviews and discussions by two anonymous reviewers secured by this journal and comments from Carl Wentworth, Bob lachens, Andy Griscom, and Malcolm Ross of the U. S. Geological Survey; Derrick Coleman of Earth Tech. Long Beach. California. Catherine Skinner of Yale University gave a review of the preliminary draft that was particularly helpful. Benjamin Page and Stephan Graham both at Stanford University gave me comments which improved the geologic interpretations. Robert Beehler and Tim Moore of the Bureau of Land Management, Hollister. California, provided information on BLM studies of the Clear Creek Management Area. Richard Vance. Presi dent and John Myer. Former President of KCAC, King City made available records of their mining and the health program for their employees and produced im portant comments regarding the asbestos mining history. Much of the mineralogical data given in this paper is from Fred Mumpton who has shared his research with the author over the years. REFERENCES Atwatea. 3. F.:Trumm. D. A.. Vlnsley.J.C. I.; Stein. R. S.:Tl'cxek. A. B.: Donahue. D. J.: ,`utu A. I.T.: and Payen. LA.. 1990. Alluvial Plains and Earthquake Recurrence at the Coatinga Anticline, U S. Geologies. Survey Professional Paper MSI: U. S. Geological Survey. Denver. CO. pp. 273-297. Bate. M. A.. 1984, Sedimentary Facies and Depositional En vironments of the Big Blue Formation Between Anticline Ridge and Oomingme Ranch: Pacific Section of the Society of Economic Psleomologists and Mineralogists (SEPM), Guidebook Vol. 3. pp. 81-85. 3 arnes. LLaMakche. V.C.: andHduielbexg.G.. 1967.Geochemi cal evidence of present day serpentinizalion: Science. Vot. 156. pp. 830-832. 3octo*. N. Z-: Siuhh. Y.N.: and Kuuexud. G.. 1987. Mercury ores from (he New Idria mining district, California: geochemical and stable isotope studies. Ceoclumicae et Cosmochimica Acta. Vol. 51. No 6. pp. 1705-1715. 8*abb. E. E,, 1991. The world landslide problem; Episodes, Vol. U. No 1. pp. 52-61 '' Bbicht, J. H.. 1965, The California asbestos industry, m Southwest Mineral Industry Conference, Sparks. Nevada. Nevada Bu reau of Mines Report. Vol. 13. No. pan B Nevada Bureau of Mines. Reno. NV. pp. I--10. KCAC Inc.. 1995, Personal communication. March. Dick Vance. President. KCAC Inc.. P. 0 Bor K. King City. CA 93930 Cambell. W.J :Hl'CCI.vs.C. W.. and Wyue.A.G.. 1978. Chemical and Physical Characterization of Amostte, Chrysatile, Cro- ctdolite, and Nonfibrous Tremoiitefor Oral Ingestion Studies by the National Institute of Environmental Health Sciences. Nevada Bureau of Mines Report of Investigation. No. 3452. Nevada Bureau of Mines. Washington, DC. 63 p. Carlson. C. 1984. Depositional facies of sedimentary serpcnti- nite: selected examples from the Coast Ranges. California, m (he Pacific Section of the Society of Economic Paleontolo gists and Mineralogists GuideOook, Field Trip No. 3. Vol. 3. pp. 73-126. - Casey, T. A. L. and Dickinson. W R,, 1976. Sedimentary serpenunite of the Miocene Big Blue Formation near Cantua Creek. California: American Association of Petroleum Geologists Bulletin. Vol. 60. No. 12. p. 2177. Churc. A. L- 1986, Asbestos content in long-term residents of a chrysolite mining town: American Review of Respiratory Disease. Vol. 134, No. I. pp. 125-127. Coleman, R. G.. 1957. Mineralogy and Petrology ofthe New fdna District. California: Unpublished Ph.D. Thesis. Department of Geology. Stanford University. Stanford. CA. 166 p. Coleman, R. G.. 1971. Petrologic and geophysical nature of scr- penttnites: Geological Socien of America Bulletin. Vol. 82. pp. 897-918. ` Coleman, R. G., 1980. Tectonic inclusions in serpentinites: Ar chives des Science Geneve. Vol. 33. pp. 39-102. Coleman, R. G.. 1986. New idria area. California (Field Trip Guide Book), in l-fth General Meeting of the International Mineralogical Association, Stanford, CA, 36 p. Coleman, R. G. and Jove. C, 1993. Geological origin of serpen tinites, In Proctor. J.; Baker. A. J. M.: and Reeves, R- D. (editors). The Vegetation of Ultramafic (SerpentineI Soils: Intercept. Andover. U. K.. pp. [-17. Coleman, R. G. and Keith. T. E., 1971, A chemical study of serpentinizalion, Burro Mountain. California: Journal of Pe trology, Vol. 12. pp. 3U-32S Coobek. W* C.: Mcrchio, J.; and Wenk. H. R.. 1979, Chrysatile asbestos in a California recreational area: Science, Vol. 206. No. 4419, pp. 685-688. Cowan. D. S. and Mansfield. C. F.. 1979. Serpentimte flows oa Joaquin ridge, southern Coast Ranges. California: Geologi cal Society of America Bulletin, Vol. 81, No. 9. pp. 26)52628. ' D'Acostlno. R. and Wilson. R.. 1993. Asbestos: The hazard, the risk, and public poficy. In Foster. K. R.: Bernstein. D. E.: and Huber, P. W. (editors). Phantom Risk: The MIT Press. Cam bridge. MA. 457 p. Dibbles. T. W,, 1971. Geologic maps ofthe Coatinga. Joaquin Rocks. New Idria. Hernandez Valley, Panache Valley, Preist Valley, U. S. Geotogcal Survey. Open File Maps (Scale 1:62.500): U.S. Geological Survey. Denver, CO. Dickinson, W. R. and Casey.T. A. L. 1976. Sedimentary serpentinite of the Miocene Big Blue Formation near Cantua Creek. California. In Fitlsche. A. E.: Ter Best. H. Jr.; and Womardt, W. W.. Tectonics and Geologic history of the Pacific Coast 20 Environmental Engineering Geoscience. Vol. (I. No. I. Spring 1996. pp. 9-22 New Idna Serpentimte of North America, Uie Neogene symposium: selected techni cal papers on paleontology, sedtmeniology. petrology: 91st Annual meeting of the Pacific Section of the Society of Economic Paleontologists, and Mineralogists (SEPM), San Francisco. CA. pp. 65-74. Ecxel. E. B. and Myers, W. B.. 1946. Quicksilver deposits of the New Idna district. San Benito and Fresno counties. Califor nia: Bulletin ofthe California Division ofMines and Geology. Vol. 42. pp. gl-124 GtA.HA.st. S rerhah A. 1995. personal communication. Professor of Geology, Department of Geological and Environmental Sci ences. Stanford University. Slanfotd. CA 94305-2225 Graham, S. A.; Stanley. R.G.. Bent, J.V.; and Carter. i.B., 1989, Otigocene and Miocene paleogeography ofcentral California and displacement along the San Andreas fault: Geological Sociery of America Bulletin, Vol. 101, pp. 711-730. Ghiscom. A. a so Iachess. R. C, 1990. Tectonic Implications of Gravity and Magnetic Models Along East-West Seismic Pro files Across the Great Valley Near Coalinga. U. S. Geological Survey Professional Paper 1487: U. S. Geological Survey, Denver, CO. pp. 69-78. Harp. E. L. and Keefe*. D. K.. 1990. Landslides Triggered by the Earthquake. U.S. Geological Survey Professional Paper 1487: U.S. Geological Survey. Denver. CO. pp. 335-347. Harrison. C. G. A.. 1994, Rates of continental erosion and moun tain building: Geol Rundsch, Vol. 83. pp. 431--147. Hastey, E. L.. 1994. Clear Creek Management Area Resource Management plan and Environmental Impact Statement (draft): Bureau of Land Management. U. S. Department of Interior, Hollister. CA. Hopson. C. A.; Mat-tinson, J. M.: and Pessagno. E. A.. 1981. Coast Range ophiolite. 'western California. In Ernst. \V. G. (editor). The Geotectonic Development of California. Vol. 1: Prentice- Hall. Englewood Qiffs. NJ, pp. 418-510. Hostetler. P. B.; Coleman, R. G.; Mcmpton, F. A.: and Evans. B. W,, 1966, Bructie in Alpine serpentinites: American Miner alogist. Vol. 51. pp. 75-98. Irwin, W. p,, 1977, Ophiolitic Terrenes ofCalifornia, Oregon, and Nevada. State of Oregon Department of Geology and Mine ral Industry Bulletin, Vol. 95: Oregon Department of Geol ogy and Mineral Industry. Portland. OR. pp. 75-92 Kanareic. M. S.; Conforti, P. M.; Jackson. L. A.: Cooper. R. C.: and Murcho. 1. C, 1980. Asbestos in drinking water and cancer incidence in the San Francisco Bay area: American Journal of Epidemiology. Vol. 112. No. 1. pp. 54-72. K.CAC Inc., 1995, Personal communication. March. KCAC Inc.. ?. O. Sox K. King City. CA 93930. Kruckeberc, A. R.. 1984, California serpentinites: flora, vegeta tion. geology, soils, and management problems: University of California Publications in Botany, Vol. 78. 168 p. Lockwood. J. P.. 1971. Sedimentary and gravity-slide emplace ment of serpentimte: Geological Society ofAmerica Bulletin, Vol. 32. No. 4. pp. 919-936. ' Loney. R. a.; Himmeumc. G. R.: and Coleman, R. G.. I97|. Structure and petrology of the Alptne-type Peridotite at 3urro Mountain. California. USA: Journal ofPetrology, Vol. 12. pp. 245-309. McDonald. 1. C.. 1985. Health implications of environmental exposure to asbestos: Environmental Health Perspectives. Vol. 62. pp. 319-328. McDonald. J. C. ano McDonald. A. D.. 1995. Chrysotile. tremo- lite. and mesothelioma: Science (letter). Vat. 267. pp. 778 779. ' Merritt, P. C.. 1962. California asbestos goes to market: Mining Engineering. Vol. 14. pp. 57-60. _ Mumpton. F. A. and Thompson. C. S.. 1966.The stability ofbrucite in the weathering zone of the New Idria serpenimite. in Fourteenth National Conference an Clays and Clay Minerals. Berkeley. CA. pp. 249-257. Mcmton. F. A. aso Thomrson. C. S.. 1975. Mineralogy and on gin of the Coaltnga asbestos deposit: Clays and Clay Minerals. Vol. 23. po. 131-U3. Munro. R. C. and Reim. K. M.. 1962. Coaimsa asbestos fiber, a newcomer to the jsbestos industry: Canadian Mining Jour- not, August, pp. 45-50. Namson, }. 5.; Davis. T. L.. and Lagoe. M. B., 1990. Tectonic History and Thrust-Fold Deformation Style of Seismtcally Active Structures Near Coalinga. U. S. Geological Survey Professional Paper 1487: U. S. Geological Survey. Denver. CO. pp. 79-96. Newkouse. M. 1. and Scujvan. K. R.. 1989. A mortality study of workers manufacturing friction materials. 1941-86: British Journal ofIndustrial Medicine, Vol. 42. No. 6, pp. 397-402 Nilsen. T. H. and Dibblee. T. W. J,, 1979. Geology of the Central Diablo Range Between Hollister and New. Idria. California. Field Trip Guide Book: Geological Society of Amenca. Cordilteran Section Meeting. San Jose, CA. 106 p. National Acaoemy of Science. 1984, Asbcstiform Fibers: Nonoccupanonal Health Risks: National Academy of Sci ence. Washington, DC. 334 p. New York Academy of Science, 1979, Health hazards of asbestos exposure, in Health Hazards ofAsbestos Exposure. Vol. 330New York Academy of Science. New York. NY. Ohlson, C. G. ano Hogsteot. C 1985. A Swedish cohort study and review: British Journal of Industrial Medicine. Vol. 39. No. 3. pp. 273-276. PACe, B. M. ano Stood*. T. M. 1993. Thrusting of the central California margin over the edge of the Pacific plate during the transform regime: Geology. Vol. 21. pp. 635-638. PofSNOORF. W. lno Wens. H.-R.. 1983, Chrysotile asbestos in a vehicular recreation area: a case study. In Webb. R. H. and Wtlshire. H. G. (editors). Environmental Effects of Off-Road Vehicles: Impacts and management in And Regions: SpringcrVerlag. New York. NY. pp. 375-396. Proctor. I.: Baker. A. J. M.: ano Reeves. R. D.. 1993. The Vegetation of UUramafic (Serpentine) Soils: Intercept, An dover, U. K., 480 p. PTt. 1992. Human Health Risk Assessment for the Clear Creek Management Area: PTl Environmental Services. PTl Con tract CS71-08 for U. S. Bureau of Land Management. Hol lister. CA. FT!. 1993. Erosion and Sedimentation in the Clear Creek Water shed. San Benito River Basin. Central California: PTl Envi ronmental Services. PTl Contract C871-09 for U. S. 3ureau of Land Management. Hollister. CA. Rextschler. M. S- 1989. Cenozoic Tectonics of the Southeastern Coast Ranges and San Joaquin Bttsiit, California: Unpub lished Ph.D. Thesis, Geology Department. Stanford Univer sity. Stanford, CA. 167 p. Rjcs.S.J- 1963. California Asbestos Industry, California Division of Mines and Geology Mineral Information Service. Vol. 16. No. 9: California Division of Mines and Geology. Sacra mento. CA. pp. 1-7. Robertson. A. H. F.. 1989. Paleoceanography and tectonic setting of the Jurassic Coast Range ophiolite. centra! California: evidence from extrusive rocks and the votcanidasuc sedi ment cover: Marine and Petroleum Geology. Vol. 6. pp. 194-219. Ross. M,, 1993. Mineral dusts, chemicals, chronic disease, and cancer: the dose makes the poison: Geologteal SocietyofAme rica Abstracts with programs. Annual meeting, Boston. MA. Ross. M.. 1994. The New [drta serpentimte of California: A tone Environmental Jc Engineering Geoicience. Vol. II. No. I, Spring 1996. pp. 9--22 UCAREF00024253 Coleman rock?- Geological Society of America Abstracts with Pro grams. V0I. 26. No. 7, p A32Q. Rtmer. M. 1 ano Ells^okth. W L.. i 990. The Coalinga, Califor nia. Earthquake of May 2. 1983, U. S. Geological Survey Professional Paper 1487: U. S. Geological Survey. Denver. CO. 417 p. SeuicoP?. 1. 1. amo Lee. D. H. K.. 1979. Asbestos and Disease: Academic Press, New York. NY. Skinner. H. C. W. *no Ross. M.. 1988. Fibrous Minerals, Mining, and Disease. Geological Society of America Report on Ge ology and Public Policy: Geological Society of America. Boulder. CO. No. 012. Skinner, K. C. W. and Rqss. M,, 1994. Minerals and cancer Geottmes. Vol. 39. No. 1. pp. 13--14. Sreiv, R. S. and Kino. G. C. P,, 1984. Seismic porentiaf revealed by surface folding: 1983 Coalinga, California, earthquake: Science. Vol. 224. pp. 869-871. TAn.OR. D,, 1990. Ecology and Ufe-History of the San Benito Evening Primrose (Camissonial, 13. S. Bureau of Land Man agement. Contract. NoCA9SO-rfp7-l3 3-325: U. S. Bureau of Land Management. Washington. DC. Thomas. H. F.; Beniamin, !. T.: Elwooo. P. C.; anoSweetnam. P.M.. 1982. Further follow-up study of workers from asbestos cement factory: British Journal ofIndustrial Medicine. Vol. 39. No. 3. pp. 273-276. Walter. A. W.. 1990. Upper-Cnuial Velocity Structure Near Coa linga. as Determined From Seismic-Refraction Data. U. S. Geological Survey Professional Paper 1487: U. S. Geological Survey. Denver, CO. pp. 23-40. Wes, R. H. ano WiLSMute, H. G.. 1983, Environmental Effects of Off- Road Vehicles: Impacts and Management in Arid Regions: Springer-Verlag. New York. NY. 534 p. Weill. H.; Hughes. 3.; ano Wacgeseack, C.. 1979. Influence of dose and five types of respiratory malignancy risk in asbestos cement manufacturing: American Review ofRespiratory Dis ease, Vol. 120. No. 2. pp. 345--354. Wentworth, C. M. ano Zoracic. M. D., 1989. The style of late Cenozoic deformauon m ihe eastern front of the California Coast Ranges: Tectonics, Vol. 8. pp. 237-246. Wentworth, C. M. .:o ZoraCk. M. D., 1990. Structure of the Coalinga Region and Thrust Origin ofthe Earthquake, 13. S. Geological Survey Professional Paper 1487: U. S. Geolo gical Survey. Denver, CQ. pp. 41-68. Wentworth. C. M.; Blake, M. C. 3.; Jones. D. L.; and Walter, a. W.. 1984. Tectonic wedging associated with emplacement of ihe Franciscan assemblage. California Coast Ranges. In Blake, M. C 3. (editor). Franciscan Geology of Northern California: Society of Economic Paleontologists and Miner alogists, Pacific Section. Los Angeles. CA. pp. 163-173. Wentworth. C. M.: Iachens. R. C.. Ststrsow. R. W.: ano Michael, A. 3., 1992. Structure of ihe Partfield region. California, from geology and geophysics compiled in a Geographic Informa tion System; Transactions, American Geophysical Union, Vol. 73. p. 396 Wicks. F. 3. ano O'Hanley. D. S,, 1988, Serpentine minerals: structures and petrology: Reviews in Mineralogy, Hydrous Phyllosilicates. American Mineralogist. Vol. 19. pp. 91-167. Woodward ano Clyoe, 1989. Characterization of Disturbances Related to Mining and Exploration in the New Idria/Coalinga/Table Mountain Study Region, report prepared for the U. S. Environmental Protection Agency under contract No. 68-W9-0020: Woodward and Clyde. Sait Francisco. CA. Woolsey, W. 3.. 1922. Asbestos in California: Pacific Mineral News, Vol. 1. No. 4. pp. 104-106. 22 Environmental & Engineering Geoscience. Vol. 11. No. 1. Spring 1996. pp. 9-22 UCAREF00024254