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POTENTIALLY ACTIVE VOLCANIC ZONES IN

Charles W. Chesterman, Senior Scientist (retired) California Division of Mines and Geology and Curator of Mineralogy, California Academy of Sciences San Francisco, California

ABSTRACT zones and 18 other volcanic zones whose latest eruptions are known (or presumed) to Volcanic activity has played a dominant be Quaternary in age, but had not erupted in role in California's long geologic history. the last 2,000,000 years, constitute the Records in rocks of many ages demonstrate known potentially active volcanic zones in that volcanic activity commenced in the California. Precambrian as early as 1.7 billion years ago, and has continued almost continuously into the present century. A review of the INTRODUCTION Geologic Map of California is sufficient to indicate the widespread distribution of Volcanism has been very active and volcanic rocks and source areas, except in prominent almost continuously throughout the Great Valley, where the cover of soils California's geologic history, commencing as and sedimentary rocks may mask other early as 1.7 billion years ago in the Pre- possible volcanic centers. cambrian and extending into the twentieth century. It has manifested itself through Advances in geophysics and geochemistry the extrusion of tremendous volumes of have demonstrated the close relationships volcanic rocks as flows and fragmental between zones of volcanic activity and deposits, and the intrusion of dikes, domes, movements of tectonic blocks. Zones of plugs, and sills. volcanic activity in the and the Coast Range provinces in California can Time and the erosive forces of running be explained through a mech- water, moving ice and air, and of gravity anism, whereas similar zones in the Mono have obliterated much of the evidence of Basin-Long Valley region of Mono County, volcanic activity, but thick deposits of the Modoc Plateau Province, and elsewhere metamorphosed volcanic rocks, of which in the and Colorado Desert some are greenstones and others, schists, provinces owe their origins to the combined form prominent geologic units ranging in effects of plate and block faulting age from early Paleozoic through late of thin continental crust. Mesozoic (an interval of some 500 million years) in the Sierra Nevada, the Klamath Five active volcanic zones in California and Siskiyou mountains, the Coastal Ranges include , , and of California, and the Mojave Desert. Medicine Lake Highland, all in the Cascade Range Province, the Mono Basin-Long In order to illustrate in a modest way the Valley region of Mono County, and the Cima extent of volcanic activity in California, in San Bernardino County. A one need only examine carefully the significant number of documented eruptions northeastern part of the state, which has occurred in these areas in the last 2,000 includes all of Modoc County and significant years. The above named active volcanic parts of Lassen, Plumas, and Siskiyou

9 counties. This is an area of approximately lacking for certain areas of the state; and 12,000 square miles, one-thirteenth of the (3) techniques of geochronology, although area of California, which is underlain by gaining stature and becoming more reliable volcanic materials ranging in age from all the time, are still not sufficiently Miocene to Holocene. Much of these advanced as to allow clear and reliable materials, totaling approxi- dating of all rocks. Because of these mately 2,400 cubic miles, were deposited factors, deposits of quaternary volcanic through explosive volcanic eruptions. rocks may be omitted or incorrectly dated on the map, and in some cases rocks of Very rarely indeed is volcanic activity an other ages may be labeled Quaternary. isolated earth process unrelated to other forces at work in the Earth's crust. On the A significant amount of data, however, is contrary, it can be demonstrated that vol- readily available, and many deposits of canic activity is and has throughout the volcanic rocks in California can be Earth's long geologic history been closely identified as being of Pleistocene and associated with , mountain Holocene ages. Holocene is here defined to building processes, and lastly and more include events since the latest glacial recently, through the interaction of gigantic (Tioga) stage. This is a variable time span plates that comprise segments of the Earth's representing, perhaps, 6,000 to 10,000 crust. years. The traditional 1,000,000 year date for the beginning of the Pleistocene has Volcanic activity in the Cascade Range been pushed back to 2,000,000 years, and in and Coast Range provinces in California is some cases further still. For rock units of best explained through the interaction approximately this age, I am using here, for between the Pacif ic plate and the North convenience, a Plio-Pleistocene time American plate, in which portions of the interval. This is a convenient slot for many former being subducted beneath the North volcanic rock units in California which are American plate are remelted and rise along not yet precisely dated. zones of weakness to the Earth's surface to result in volcanic activity. Volcanic Following Kilbourne and Anderson ( 1981), activity in the Basin and Range Province in zones of volcanic activity in California can California, which includes the Modoc be considered in three categories: (1) active Plateau-Warner Range area in Modoc -- one in which there is current volcanic County, the Mono Basin-Long Valley region activity, or which has erupted in the last of Mono County, and the Mojave Desert and 2,000 years; (2) potentially active -- one Colorado desert regions in southeastern known (or presumed ) to be Quaternary in California, is probably due to a combination age, but the most recent eruption has not of the interaction of Earth plates and the been dated as being less than 2,000 years block faulting of thin continental crust on ago; and (3) inactive -- one in which there the margin of an area undergoing extension. has been no eruption in the last 2 million years.

Since our interest for this workshop lies in ZONES OF VOLCANIC ACTIVITY IN the active and potentially active volcanic CALIFORNIA zones in California, discussion will be confined to 23 areas in the state in which Another look at the Geologic Map of rocks of Pleistocene and especially California tells one that the state has been Holocene ages occur. Frequent reference mapped geologically one way or another, but will be made to Figure 1, a map of it is not possible to identify all deposits of California which shows the areas of known quaternary volcanic rocks since: (1) geo- deposits of Quaternary volcanic rocks, and logic process do not stop conveniently at also several major tectonic features, temporal or spatial boundaries; (2) geologi- particularly faults, as they may relate to cal mapping is incomplete or even totally zones of Quaternary volcanic activity.

10 MAP OF CALIFORNIA SHOWING AREAS UNDERLAIN BY QUATERNARY VOLCANIC ROCKS-THE POTENTIALLY ACTIVE VOLCANIC ZONES

c-11',4149£•IT'*# ·•:·· Volcanic areas-zones : ,¢'1 3129 YA••f•.1, 1. Mount Shasta r0 \ ./ 1• 0 \ 46. '..- .- 'gtill#/95;WA:WEHEawbilflitili 2. Medicine Lake Highlands 2 B. 1.- LAEr. 3. Modoc Plateau 1 ( ', '1,4-.6 > 4..,$- :1 - /'isffl •:1 5-=.4 4. Mount Lassen a Vicinity 4» f-//.=•--,« 5. Eagle Lake 6. Lousetown - •r . /0 'ft'j 7. Clear Lake , ,. '• 8. Mono Basin-Long Valley \ 036" 9. Aberdeen « 1-» :7 -,1 -1., », t ./ '29 10. Coso Mountains A- '\' Fi 11. Cima I b 'fl f,•.» 12. Amboy-Pisgoh 'I042'r•t•13. Turtle Mountains V , L ,<' -, r . <·....r 4.... I . - I.\' - = .,-c:*• 14*. 14. Pinto Basin-Salton Creek = 3 « - '1&«'I .«44•/•-B., 15. Buttes 1 2 / \ '. 12 ··\. / \'.% ..is: '-Al'<"•1£,Ex, 16. Miscellaneous ,'. ,» . - -. 2<116)87 \.: \ ./ --I 33*11 &*.>ey \. : + I -, 1---- -t ···. .r·-F ,. - Faults tAL•, . \. • T U 9.6,4..,•2•••• ---A,- .4 1 l Aii'Oi:•8 i - merN - \ 7. 0 1' --- -.---.--. -163••••4•----•%6 ,--tt·•...• E AN LUIS OBISPO e 19 . Ifi'•4:*©'eaurib ' .4%8 *- -':L.f -# 4#J./.-':FLW.b:. '.. a3», 1. .- - 6 - f -i --1 •te) 1:1.:.:.:.:.I.P.3...''.'. ''.''.. \ ij•.E:.ES k.., .-C. 461 -3 \...: F > tf 49%%7.- -:. X•<:15-9. f.. ) Figure 1 - 11 POTENTIALLY ACTIVE VOLCANIC Holocene time ( 660 A.D. + 240 years) ZONES IN CALIFORNIA resulted in the mantling of-the area by rhyolitic pumiceous tephra -- deposition of The following discussion will consider the which was followed by the emplacement of potentially active volcanic zones in obsidian domes and the development of California, their geographic locations, types cinder cones. More than 100 cinder cones of volcanic products, and physical features, developed during the Holocene volcanic and will commence with those zones in the episode, and at least 20 cones during the northern part of the state and conclude with Pleistocene. a group of miscellaneous small zones that are largely in southeastern California. Modoc Plateau (Area 3). This area is wholly in Modoc County and includes the Mount Shasta (Area 1 ). Mount Shasta, a Warner Range. It has been the focus of complex stratocone and the largest of the intensive volcanism since the Miocene. In , is in the central part of 1954, there was a violent - Siskiyou County. It is composed of eruption on the east side of the Warner Pleistocene and flows, and Range near Lake City. Numerous basaltic pyroclastic deposits, and Holocene basalt cinder cones dot a plateau-like surface that and andesite flows, domes and is underlain by numerous flood basalt flows. pyroclastic deposits. A major north-south fracture zone that passes through the Mount Lassen and Vicinity (Area 4). volcano, has controlled the location of Although Lassen is in Shasta County, the cinder cones and plug domes. , a general area herein considered is largely in Holocene cone high on the west flank of eastern Shasta County but includes small Mount Shasta, contains a central plug dome portions of adjacent Lassen, Plumas, and of dacite, and was the source of voluminous Tehama counties. The area was the site of pyroclastic-flow deposits that cover many extensive out-pourings of basalt and square miles on the west side of Mount andesite flows during the Pliocene and Shasta and reach points beyond the town of Pleistocene. Later, a large stratocone Weed. Similar pyroclastic-flow materials named "" developed as the issued forth from Black Butte, a composite result of subsequent volcanic activity. of four dacite domes of Holocene age, and Much later, and dacite intruded the were deposited to the sou thwest as far as flanks of Mount Tehama, flows of dacitic Lake Siskiyou. There are 13 Quaternary lava erupted from vents near Lassen Peak cinder cones, remnants of five Pliocene and, much later still, the dacite plug dome cinder cones, and Holocene flows from which forms Lassen Peak was emplaced. Shastina and Hotlum cones. Perhaps the The eventual collapse of Mount Tehama most recent eruption in the area occurred in formed a in which one can now find 1786. hot springs and extensive fumarolic action.

Medicine Lake Highland (Area 2 ). During the Holocene, perhaps not more Medicine Lake Highland is in eastern than 1,200 years ago, violent eruptions Siskiyou County and western Modoc blasted forth from an eruptive center north County. The highland is a rampart of small of Lassen Peak and produced hot volcanoes ranging from late Pleistocene to pyroclastic-flows and pumiceous tephra. Holocene in age perched upon a low, Shortly thereafter, a group of dacite domes, broad- of Pliocene and now called , were emplaced in Miocene basalt and Pleistocene pyroclastic the same eruptive center. deposits. The lava flows and pyroclastic deposits of the cone were intruded by In 1851-52, an eruption of basalt rhyolite, and collapse of the central part of lava, a few miles northeast of Lassen Peak, the cone along a set of arcuate fractures, gave rise to a (called Cinder gave rise to a caldera which now contains Cone) and lava flows. More recent activity Medicine Lake. Violent eruptions in in the Mount Lassen area, commencing in

12 1914 and culminating in 1917, was of the basalt, rhyolite, and pyroclastic deposits. explosive type and is very well documented. The Pleistocene was a period of almost continuous volcanic activity extending to There are over 30 cinder cones of Plio- the present. A major eruption about Pleistocene age in the area, and current 700,000 years ago gave rise to the Bishop activity is restricted to hot springs and and the formation of Long Valley cal- . dera. The Mono Basin-Long Valley region has experienced at least 30 pumiceous Eagle Lake ( Area 5). This area lies tephra and lava eruptions in the past 2,000 almost wholly in Lassen County, and is years, and all were of . Many underlain by numerous flood basalt flows of hot springs and several steam wells occur at Pliocene and Holocene ages. The latest and near the Casa Diablo thermal area, and eruptions of, perhaps, Holocene age were the latest eruption may have taken place basaltic lava flows in the vicinity of Eagle beneath the waters of Mono Lake as late as Lake. At least 30 cinder cones of 1890. Ouaternary age occur in the area. Aberdeen (Area 9 ). The Aberdeen Lousetown ( Area 6). This area occurs volcanic field is in Owens Valley at the base north of Lake Tahoe and is in the eastern of the Sierra Nevada in west-central Inyo parts of Nevada and Placer counties. It is County. It contains flows and cones of ba- underlain largely by flows of basalt and salt of Holocene or late Pleistocene age, of early Pleistocene age, which are and a dome of perlitic rhyolite of Pleisto- said to have a K/Ar age of 1 -2 million years cene age, all of which lie partly on alluvium. B.P. There were explosive eruptions in the area as evidenced by remnants of eight Coso Mountains (Area 10 ). The Coso cinder cones. Mountains are at the southern end of Owens Valley in Inyo County. This area has been Clear Lake (Area 7). The Clear Lake the site of explosive volcanic eruptions volcanic field is in southern Lake County starting some 11 million years ago and and northeastern Sonoma County. It culminating about 40,000 years ago. There includes the well-known Geysers geothermal are 35 rhyolite domes, 19 basaltic cinder field. Flows of basalt, andesite and rhyo- cones, and significant deposits of pumiceous lite, and rhyolitic tuffs of Pleistocene age tephra lying on or near the surface of the occur in the area. Rocks of Holocene age ground. Current activity includes fumaroles include obsidian, andesite, dacite, and four and hot springs at the Coso Hot Springs cinder cones. The occurrence of sulfur and thermal area. extensive mercury mineralization at Sulphur Bank; deposits of sulfur on Mount Konocti; Cima ( Area 11 ). The , and the high concentration of boron at located in the northeastern part of San Borax Lake all indicate recent volcanic Bernardino County, contains basaltic cinder activity. The hot springs, fumaroles, and cones and lava flows of Pleistocene age, and steam wells at the Geysers and vicinity are lava flows as well as 27 cinder cones of clear indications that a significant source of Holocene age. The Holocene cones and lava heat, which is undoubtedly related to flows rest on alluvium, and the youngest of volcanic action, is still present in the area. the Holocene rocks has been dated at about 360 years. Mono Basin-Long Valley (Area 8). This area of high potential volcanic activity Amboy-Pisgah (Area 12 ). This area is in occurs largely in Mono County. Cenozoic the central part of San Bernardino County volcanic rocks of Oligocene and Miocene and centers principally about Pisgah Crater ages (radiometrically dated as 11 to 29 and , which are separated by million years old) include andesite, dacite, some 40 miles of arid lands. Holocene rhyolite, and welded tuff. Between 3 and 12 basaltic cinder cones and lava flows, and million years ago, discontinuous volcanic Pliocene andesitic and basaltic dikes, lava activity resulted in the eruption of andesite, flows, plugs and sills occur in the region.

3-76977 13 i Because of the fresh appearance of their CONCLUSIONS lavas, Amboy and Pisgah craters are thought to be less than 2,000 years old. The above listed areas contain the known, potentially active volcanic zones in Turtle Mountains ( Area 13). The Turtle California wherein hazardous conditions are Mountains, which contain flows of most likely to occur. However, one cannot Pleistocene basalt lying on late Tertiary be absolutely certain that this list is volcanic rocks, are in the southeastern part complete, for, as was stated earlier, there is of San Bernardino County. The late a likelihood (remote as it may be) that there Tertiary volcanic rocks contain layers of are isolated bodies of Holocene volcanic pyroclastic deposits and perlitic rhyolite rocks that have been erroneously included flows, which indicate that the area has been among older volcanic units. These the focus of explosive volcanic eruptions. improperly identified bodies might just as well be sites for future volcanic activity as Pinto Basin-Salton Creek ( Area 14). are any of the five zones that are Remnants of Pleistocene or Holocene considered among the most active in the basaltic flows and pyroclastic deposits lie on state. alluvium in the Pinto Basin and Salton Creek areas in central Riverside County.

Obsidian Buttes ( Area 15). This area, in DISCUSSION Imperial County near the southern end of , contains obsidian domes and McBirney: I notice that the Sutter Buttes pumiceous tephra deposits of late were not mentioned in your talk. Do you Pleistocene age amid alluvium and consider them too old, and if so, what is the lacustrine sediments. The area contains hot youngest age that has been obtained there? springs, springs and wells, and mud volcanoes. Several thermal wells encountered hot brines. Chesterman: I didn't mention them as being active because they are rather old. I Miscellaneous ( Area 16). Scattered believe their youngest age is about 1.4 throughout the Basin and Ranges Province in million years old. Inyo, Imperial, Kern, Riverside, San Bernardino, and San Diego counties are a number of bodies of volcanic rocks, Question: What is the approximate age of consisting principally of flows of andesite the volcanic tubes at Cambria, north of and basalt, and pyroclastic materials, all Morro Bay? ranging in age from late Pliocene to Holocene. Included among the bodies are: lavas in the El Paso Mountains in eastern Chesterman: Any volcanism in that part of Kern County; basaltic flow remnants on the state is likely to be either late Miocene pyroclastic deposits in the Fort Irwin area or early Pliocene in age. As one proceeds and at Opal Mountain, northeast and from the southern part of the California northwest of Barstow respectively; small Coastal Ranges northward, the age of remnants of a probable Pleistocene basalt volcanic rocks becomes progressively flow northeast of Ogilby, Imperial County; younger. Volcanic rocks in the Morro Bay and possible Pleistocene basalt flows on area are of late Miocene/early Pliocene age pyroclastic deposits near Murrieta, while to the north, in Lake County, some Riverside County. volcanic rocks are as young as very late Pleistocene, or about 11,000 years old. An extensive area in central Inyo County contains flows and pyroclastic deposits of Pliocene and/or Pleistocene age, as well as Question: Just how active is the Surprise a Holocene basaltic and Valley area? I heard about a mud volcano rhyolitic ash deposits. being in that area. Could y'ou explain that?

14 Chesterman: Mud volcanoes erupted in Chesterman, Charles W., 1971, Volcanism in Surprise Valley at hot springs near Lake California: California Geology, v. 24, City, Modoc County in 1951 and 1953. P. 139-147. There is extensive faulting in the area, and although the springs owe their high Chesterman, Charles W., 1955, Age of the temperature of about 65 ° C and part of their obsidian at Glass Mountain, Siskiyou water supply and mineral content to past County, California: American Journal of volcanism, it seems unlikely that their Science, v. 253, p. 418-424. mud-volcano activity of comparatively recent date is a forerunner of future Crandell, D.R., Mullineaux, D.R., Sigafoos, volcanic activity. R.S., and Rubin, M., 1974, Chaos Crags eruptions and rockfall-avalanches, Lassen Question: How about the Aberdeen area? Volcanic National Park, California: Journal of Research of the U. S. Geological Survey, v. 2, n. 1, p. 46-60. Chesterman: The Aberdeen volcanic area is located in Inyo 254ountyalong a frontal fault Dickinson, W.R., 1979, Cenozoic plate zone of the Sierra Nevada. It is an area tectonic setting of the Cordilleran region where rocks of both rhyolitic and basaltic in the United States, i!1 Armentrout, John compositions erupted from nearby vents. M., Cole, Mark R., and Ter Best, Harry The basaltic eruptions formed cinder cones Jr., editors, 1979, Cenozoic paleogeogra- and lava flows while the rhyolitic eruptions phy of the western United States Pacific have given rise to domes of perlitic rhyolitic Section, Society of Economic Paleon- and tuffs. A late Pleistocene or early tologists and Mineralogists, Los Angeles, Holocene age has been determined for one P. 1-13. of the cinder cones. Finch, R.H., 1930, Activity of a California volcano in 1786: The Volcano Letter, REFERENCES n. 308, p. 3.

Alfors, J.T., 1980, Regional geology of the Harkness, H.W., 1975, A recent volcano in Mammoth Lakes region, California, in Plumas County: California Academy of Sherburne, R.W., editor, 1980, Mammot Science, Proceedings, v. V, 1873-1874, Lakes, California earthquakes of May p. 408-412. 1980: California Division of Mines and Geology Special Report 150, p.1-6. Katz, Marvin, and Boettcher, Art, 1980, The Cima volcanic field, in Fife, D.E. and Anderson, C.A., 1941, Volcanoes of the Brown, A.R., editors, 1980, Geology and Medicine Lake Highland, California: mineral wealth of the California Desert: California University Department of South Coast Geological Society, Santa Geological Sciences Bulletin, v. 25, Ana, p. 236-241. p. 347-421. Kilbourne, R.T. and Anderson, C.L., 1981, Bailey, Roy A., Dalrymple, G. Brent, and Volcanic History and "active" volcanism Lanphere, Marvin A., 1976, Volcanism, in California: California Geology, v. 34, structure, and geochronology of Long p. 159-168. Valley Caldera, Mono County, California: Journal of Geophysical Research, v. 81, Kilbourne, R.T., Chesterman, C.W., and n. 5, p. 725-744. Wood, S.H., 1980, Recent volcanism in the Mono Basin-Long Valley region of Mono Birkeland, Peter W., 1963, Pleistocene County, California, in Sherburne, R. W., volcanism and deformation of the Truckee editor, 1980, Mammdh Lakes, California area, north of Lake Tahoe, California: earthquakes of May 1980: California Geological Society of America Bulletin, Division of Mines and Geology Special v. 74, p. 1453-1464. Report 150.

l 15 Parker, Ronald B., 1963, Recent volcanism White, Donald E., 1955, Violent mud-volcano at Amboy Crater, San Bernardino County, eruption of the Lake City hot springs, California: California Division of Mines northeastern California: Geological and Geology Special Report 76. Society of America Bulletin, v. 66, p. 1109-1130. Proffett, John M., Jr., 1977, Cenozoic geology of the Yerington District, Williams, Howel, 1932, Mount Shasta, a Nevada, and implications for the nature Cascade volcano: Journal of Geology, and origin of Basin and Range faulting: v. 40, p. 417-429. Geological Society of America Bulletin, v. 88, p. 247-266. Williams, Howel, 1932, Geology of the Lassen Volcanic National Park, Cal- Rinehart, C. D., and Huber, N. King, 1965, ifornia: California University Department The Inyo Crater Lakes--a blast in the of Geological Science Bulletin, v. 22, past: California Division of Mines and p. 193-385. Geology Mineral Information Service, v. 18, n. 9, p. 169-172. Williams, Howel, 1949, Geology of the Macdoel quadrangle, California: Califor- Shelton, John S., 1954, Miocene volcanism in nia Division of Mines Bulletin 151. coastal southern California: California Division of Mines Bulletin 170, ch. VII, p. 31-36.

Townley, S.D., and Maxwell, W.A., 1939, Descriptive catalogue of earthquakes of the Pacific Coast of the United States: Seismological Society of America Bulletin, v. 29, p. 83.

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