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- I OAK RIDGE NATIONAL Lagef CONTROL POST OFFICE BOX X OAK RIDGE, TENNESSEE 37831 OPERATED BY MARTIN MARIETTA ENERGY SYSTEM T E IRW December 14, 1984
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Docket No. _
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Dr. D. J. Brooks (Return to WMl, 623-SS) _____ -3- Geotechnical Branch Office of Nuclear Material Safety and Safeguards U.S. Nuclear Regulatory Commission 623-SS Washington, D.C. 20555
Dear Dave:
Enclosed is a copy of Jim Blencoe's and Gary Jacobs's trip report (MR-287-1) to attend the Geological Society of America meeting in Reno, Nevada, on November 2-10, 1984.
Sincerely,
Susan K. Whatley, Manager Repository Licensing Analysis and Support Chemical Technology Division
SKW:kk
Enclosure
cc: J. W. Bradbury, Geotechnical Branch W. Dam, Geotechnical Branch W. R. Kelly, Geotechnical Branch L. Kovach, Geotechnical Branch R. J. Starmer, Geotechnical Branch J. G. Blencoe N. H. Cutshall L. M. Ferris G. K. Jacobs A. D. Kelmers A. P. Malinauskas SKW File
g TRIP REPORT OF GEOLOGICAL SOCIEITY OF AMERICA MEETING AT RENO, NEVADA AUTHORS: J. G. Blencoe and G. K. Jacobs LOCATIONS: Nevada Test Site (pre- and post-meeting field trips) and Reno, Nevada (GSA Annual Meeting) DATES: Pre-meeting field trip--November 2-4, 1984; GSA Annual Meeting--November 5-8, 1984; Post-meeting field trip--November 8-10, 1984 PURPOSE: Participate in field trips to the Nevada Test Site, and attend the Annual Meeting of the Geological Society of America. PROJECT TITLE: Technical Assistance in Geochemistry. PROJECT MANAGER: S. K. Whatley. ACTIVITY NUMBER: ORNL #41 37 54 92 4 (189 #B0287)/NRC #50 19 03 01. SUMMARY This report describes the activities and experiences of J. G. Blencoe and G. K. Jacobs during: (1) pre- and post-meeting field trips to the Nevada Test Site (NTS), and (2) the annual meeting of the Geological Society of America (GSA). The pre-meeting field trip, attended by J. G. Blencoe, was conducted to examine the geology of the NTS. The post- meeting field trip, attended by G. K. Jacobs, was undertaken to review the regional flow systems, groundwater recharge, and unsaturated flow within the NTS and adjacent areas. The GSA Annual Meeting was attended by both J. G. Blencoe and G. K. Jacobs. GENERAL OBSERVATIONS AND COMMENTS ON THE GSA MEETING AT RENO The 1984 GSA Annual Meeting was held in the MGM Grand Hotel in Reno, Nevada, on November 5-8. Approximately 6,000 geoscientists were present at the meeting, making it the most well-attended GSA annual meeting ever. Symposium on the Geology, Hydrology, and Geochemistry of the NTS 2:00 p.m., November 5, 1984) In addition to the usual technical sessions on geoscientific subjects (petrology, paleontology, geophysics, etc.), this year's GSA Annual Meeting included a half-day symposium on the geology, hydrology, and geochemistry of the NTS. The speakers who delivered presentations at this symposium, and the titles of their papers, are: 1. Thomas R. Clark: The Role of Earth Science at the Nevada Test Site--The Manager's Viewpoint. 2 2. H. Lawrence McKague, Paul P. Orkild: Geologic Framework of Nevada Test Site. 3. Carol J. Boughton, Roger L. Jacobson, John W. Hess: Regional Groundwater Characteristics Determined From Geochemistry and Environmental Isotopes at the Nevada Test Site. 4. W. J. Carr: Timing and Style of Tectonism and Localization of Volcanism in the Walker Lane Belt of Southwestern Nevada. 5. Robert B. Scott: Internal Deformation of Blocks Bounded by Basin- and-Range-Style Faults. 6. Barney J. Szabo: Uranium-Series Dating of Fault-Related Fracture- and Cavity-Filling Calcite and Opal in Drill Cores From Yucca Mountain, Southern Nevada. 7. Christopher C. Barton: Tectonic Significance of Fractures in Welded Tuff, Yucca Mountain, Southwest Nevada. 8. Richard K. Waddell: Solute-Transport Characteristics of Fractured Tuffs at Yucca Mountain, Nevada Test Site--A Preliminary Assessment. 9. Norman R. Burkhard: Applications of Geophysical Exploration Techniques to Structural Interpretations at the Nevada Test Site. 10. J. N. Rosholt, C. A. Bush, W. J. Carr: Uranium-Trend Dating and its Application to Quaternary Deposits in the Nevada Test Site Region. 11. J. L. Wagoner, H. L. McKauge: The Alluvial Valley Fill, Yucca Flat, Nevada. 12. Clinton M. Case, Mark Kautsky, Peter M. Kearl, Diane M. Nork, Thomas F. Panian, Sarah L. Raker: Unsaturated Flow Through the Alluvium at the Nevada Test Site. 13. Stephen W. Wheatcraft, Thomas J. Burbey: Numerical Modeling of the Tritium Breakthrough at the Cambric Site, Nevada Test Site. 14. Richard H. French: Assessment of Flood Risk to Facilities Sited on Alluvial Fans at the Nevada Test Site. 15. E. M. Romney: Restoration of Vegetation in Areas Disturbed by Nuclear Testing at the Nevada Test Site. Our principal observation concerning these papers is that the speakers did not focus on information obtained recently, and most of the discussions were directed toward the hydrology and geology of the entire NTS (i.e., very little was said about the "local" hydrology, geology, and geochemistry of Yucca Mountain). Furthermore, many of the presentations were poorly delivered, and sometimes accompanying slides were difficult to read. 3 Miscellaneous Papers on Topics Related to Disposal of High-Level Radioactive Waste Several technical sessions held during the Annual Meeting included presentations that dealt with the geochemistry of brines at the various candidate salt sites (however, most of the discussions focused on the Palo Duro Basin site). From the talks dealing with the Palo Duro Basin site, we learned that the deep water-bearing Wolfcamp Formation is being studied extensively by the Texas Bureau of Economic Geology to determine: (1) the source(s) and age(s) of the fluids, and (2) the significance of brine chemistry for conceptual models of groundwater flow. Several technical sessions devoted to geochemical topics included interesting presentations on rock/water interactions. For example, a researcher from Stanford University described experimental work that he has performed on the solubility of UO2 at high temperatures. His data suggest that calculated solubilities of U02 at 100-300'C obtained from the thermodynamic data that is currently available may be off by as much as 3-4 orders of magnitude! There were also several papers which described work currently being performed on the mechanisms of oxidation and reduction of aqueous species at or near the surfaces of minerals. Still another interesting paper presented evidence that some form of bacteria may have been found in fluid inclusions from a geothermal area (temperatures up to 200'C). This is the first observation of this sort and it may have implications for evaluations of the significance of bacterial processes in the mobilization and retention of radionuclides released from a repository. In the past, it has been considered that bacteria would not survive the thermal period; however, it seems evident now that the validity of this assumption should be reassessed. Conclusions As expected, this year's GSA Annual Meeting included the usual mix of excellent, good, mediocre, and terrible talks. However, in our opinion, the overall "value" of the meeting is not properly assessed by considering only the number of interesting talks that were delivered during the technical sessions. In addition to being able to attend technical sessions that dealt wholely, or in part, with waste-management subjects, the meeting provided us with an opportunity to verbally exchange information with colleagues from other national laboratories and from universities who share some of our interests and concerns regarding the geochemistry of high-level waste (HLW) disposal. Such exchanges enhance our professional development in three ways: (1) we gain knowledge directly from our peers in a scientific atmosphere that encourages expression of honest opinion; (2) by meeting and talking with our peers face-to-face, we establish a positive standing and credibility among scientists who are working on HLW disposal problems; and (3) we reestablish old contacts with peers, and make new contacts, which pre- serve or open up lines of communication which can be of great value at a later time (e.g., when it is necessary to obtain new information quickly, and you are wondering who to contact to obtain this information). In view of these beneficial aspects of attending this year's meeting, we hope that the NRC will allow up to attend future GSA Annual Meetings. 4 COMMENTS ON THE PRE- AND POST-MEETING FIELD TRIPS TO THE NEVADA TEST SITE Field Trip on the Geology of the Nevada Test Site (J. G. Blencoe) a. Comments concerning events and observations on the first day of the field trip (November 3, 1984) The first day of the field trip was spent traveling from Las Vegas to Mercury (NTS) and observing the geology along the way. It was emphasized that, while the rocks around Las Vegas are Precambrian or Paleozoic in age, and contain many sedimentary lithologies, the rocks on--and adjacent to--the NTS are predominantly Cenozoic (mainly Miocene) and Recent volcanic rocks. Due to the significant distance that we had to travel, we only made a few stops to perform some "roadside geology;" the rest of the time was spent observing distant rock formations through the windows of the bus. There were no discussions of a geochemical nature at all during the day, which was disappointing. I suspected that geochemistry would not be emphasized in verbal discussions presented by our field-trip guides, mainly because the field trip was advertised as a geology field trip, but I was a little surprised that no attempts were made to present information that would have been of great interest to geochemists. (For example, it would have been very interesting to learn more about the patterns of alteration of tuffaceous rocks at the NTS.) However, the day was "saved" (from the point of view of this geochemist) by two events: a brief visit to Yucca Mountain in the early afternoon, and a tour of the USGS Core Library at Mercury at the end of the day. The visit to Yucca Mountain was rewarding because, after seeing it, I now have a good mental image of the topographic and geologic environment of the candidate-repository site at Yucca Mountain. During the brief lunch-hour stop at the summit of the mountain (Yucca Mountain is actually a broad ridge), there were detailed discussions of the regional geology and hydrology of the area, but essentially no discussion of the geochemistry of the rocks beneath the mountain. Nevertheless, the lectures delivered by the field-trip leaders were interesting, especially the presentation given by Rick Waddell of the USGS. From his talk I conclude that the hydrology of the Yucca Mountain region is still poorly understood, the principal unknowns being: (1) the rate of groundwater recharge at Yucca Mountain, and (2) the rates and volumes of fracture flow vis-a-vis matrix flow of groundwater at the site. The visit to the USGS Core Library at Mercury was the last stop of the day. This core library, officially designated "The Geologic Data Center and Core Library" at Mercury, is a depository for systematic processing, cataloguing, and storage of drill-bit cuttings, drill core, and other rock samples from the NTS and other test areas. The facility serves as: (1) a field headquarters for USGS geologists, hydrologists, and geophysicists, and (2) a work area for earth scientists employed in support of weapons testing and DOE waste-management projects. The faci- lity maintains reference files of reports, maps, aerial photographs, and downhole video tapes and geophysical logs for selected drill holes at 5 the NTS and other test areas. Water samples are analyzed both chemi- cally and radiologically in a hydrologic-chemical laboratory adjacent to the Core Library. Continuous core, sidewall samples, and rock cuttings stored at the Core Library have been used to resolve geologic problems encountered by personnel concerned with nuclear-test containment and HLW disposal. For example: (1) primary minerals and whole rocks are analyzed to help correlate volcanic units found at the Test Site, and (2) secondary (diagenetic) minerals have been studied intensively to gauge their ability to inhibit migration of radionuclides. Regarding (1), LANL geochemists are analyzing phenocryst minerals and whole rocks to model the origin and evolution of the late-Tertiary volcanic sequence at the NTS. Recent work has allowed accurate correlation of individual petrologic units as well as entire petrologic suites. The spatial distribution patterns of correlative petrographic units point to the Timber Mountain - Oasis Valley magmatic system as the primary source of Miocene volcanic rocks at the NTS. This observation, along with supporting geochemical data, indicates that Miocene volcanic rocks at the NTS are the effusive product of a single, large, evolving rhyolitic- magma body that was located beneath the present expression of the Timber Mountain Caldera. b. Comments concerning events and observations on the second day of the field trip (November 4, 1984) Like the first day of the field trip, activities on this day consisted mainly of "geologic sight-seeing." The highlight of the day was a visit to the SEDAN crater, a circular pit--approximately 390 m in diameter and 98 m deep--which was formed in tuffaceous alluvium just to the east of Rainier Mesa as a result of the detonation of a 100 kt atomic device on July 6, 1962. During the stop at this crater, there was much discussion of "containment geology" (geologic studies in support of underground testing of nuclear devices) and nuclear-excavation scaling laws (the empirical relationships between the kilotonnage of an atomic device, depth of detonation, and the size of the resulting crater produced by the explosion of the device). The only activity of the day which possessed a geochemical "flavor" was a visit to the Radionuclide Migration (RNM) project site on Frenchman Flat. The RNM project was initiated in 1974 to study the rates of underground migration of radionuclides from explosion-modified zones at the site of the "Cambric event." The Cambric event, which refers to the detonation of an atomic device beneath Frenchman Flat in 1965, was chosen for study because, among other amenable conditions: (1) sufficient tritium was present to provide an easily measureable tracer for water from the cavity region; (2) the post-shot debris and groundwater in the cavity and overlying chimney contained quantities of plutonium, uranium, and fission products that were sufficient for measurement and comparison; (3) the small nuclear yield from the Cambric event was expected to have little effect on the local hydrology; and (4) it was judged that alluvium is a good medium for radionuclide-migration 6 studies because it is more permeable than tuff and does not contain large fractures through which groundwater might selectively flow. Beginning in October, 1975, water was pumped from a satellite well located 91 m from the Cambric cavity; this produced an artificial gradient that was sufficient to draw water from the Cambric cavity, thereby providing an opportunity to study radionuclide migration under field conditions. The satellite well was pumped at the rate of -600 gal/m. Every week samples were taken and analyzed for radionuclides. The first radionuclide detected was 3 6C1. Later (in the summer of 1978), tritium was detected, and by late summer, 1980, the concentration of this radionuclide reached a peak of 7000 pCi/mL. By September 30, 1982, over 42% of the tritium from the Cambric event had been removed by the satellite well. Field Trip on the Hydrogeology of the Nevada Test Site and Amargosa Desert (G. K. Jacobs) This field trip was excellent. We observed and discussed many aspects of the flow regimes pertinent to the area (ie., alluvium, tuff, and Palezoic carbonates). There is apparently still significant controversy concerning not only the location of recharge and discharge areas, but also the potential impact of groundwater flow on the containment and isolation of radionuclides resulting from the testing of nuclear devices and the proposed repository at Yucca Mountain. Because a nuclear device was scheduled to be tested at the NTS on Friday, November 9, the field trip was run in reverse order from that described in the field trip guide. We were supposed to be able to get onto the NTS on Saturday in order to observe and discuss the hydrology of Yucca Mountain and other aspects of the NTS. As it turned out, the device was tested on the morning of Saturday, November 10. Therefore, our first stop that day was Yucca Mountain and the rest of the NTS por- tion of the field trip followed. a. Comments concerning events and observations on the first day of the field trip (November 9, 1984) The first day was spent traveling from Las Vegas to Beatty through the Amargosa Desert to observe and discuss hydrologic characteristics of the area. The Amargosa Desert is a possible discharge area for groundwaters which originate within the NTS. Groundwater discharge occurs as small springs emanating from Palezoic carbonate units. We observed a popula- tion of pupfish - "minnow-like" fish which live in the springs of the Amargosa Desert. These pupfish are significant because a large irriga- tion project in the desert was discontinued when it was shown that over- pumping of the aquifer system was lowering the level of water in the springs to a point below which the pupfish could no longer reproduce - thus endangering their existence. During the day, useful discussions concerning the regional geology and hydrology occurred with the participants and leaders of the field trip. These discussions were particularly interesting because the field trip 7 leaders were with the Desert Research Institute (DRI) and are currently involved in evaluating the hydrochemical work which is being carried out by the USGS and LANL. Apparently, DRI has access to water samples and other hydrologic data being collected by the USGS and LANL. The last stop of the day was at the U.S. Ecology waste disposal area, just outside of Beatty, NV. This facility accepts low-level radioactive waste as well as toxic chemical waste. Only solidified waste are currently disposed of at the facility. We observed and discussed the disposal practices including the segregation of wastes and the hydrology of the unsaturated zone in which the facility is located. b. Comments concerning events and observations on the second day of the field trip (November 10, 1984) The first stop was at Yucca Mountain to observe a pump test which was being conducted. We discussed the general geology and hydrology of the Yucca Mountain area, however, few details were covered. As J. G. Blencoe discussed earlier, being able to visualize the geologic and hydrologic setting of Yucca Mountain will be valuable in future review efforts con- cerning the NNWSI Project. The next major stop was at a low-level waste (LLW) site on the NTS. This site has been instrumented to investigate the hydrology of the unsaturated zone as related to the disposal of LLW. DRI is involved in many studies of unsaturated zone hydrology. Though much uncertainty remains in their understanding of the hydrology of the unsaturated zone, the residence time of water in the unsaturated alluvium is thought to be on the order of months. Therefore, it is possible that the conceptual model of NNWSI for the rapid transport of water through the unsaturated zone - thus little time for reaction with repository materials - may be realistic, although the repository will be constructed in rock, whereas most studies to date by DRI have addressed the alluvium. Also included in this field trip were stops to the SEDAN crater and the Radionuclide Migration (RNM) site on Frenchman Flat. These areas were discussed by J. G. Blencoe earlier and will not be repeated here. f NEVADA TEST SITE FIELD TRIP GUIDEBOOK 1984 (FIELD TRIP 10) Leaders: HOLLY 0. ANDER, Los Alamos National Laboratory F. M. BYERS, JR., Los Alamos National Laboratory PAUL P. ORKILD, U.S. Geological Survey With contributions from: HARLEY BARNES (deceased), W. J. CARR, WILLIAM W DUDLEY, EVAN C. JENKINS, F. G. POOLE, RALPH R. SHROBA, ROBERT B. SCOTT, and MARTHA G. VAN WERKEN, U.S. Geological Survey DAVID E. BROXTON, BRUCE M. CROWE, DONATHON J. KRIER, SCHON S. LEVY, WARD L. HAWKINS, DAVID T. VANIMAN, and RICHARD G. WARREN, Los Alamos National Laboratory. FOREWORD repository. These Investigations involved volcanic and earthquake hazard studies, The Nevada Test Site (NTS) was established detailed geochemical studies of composi- on December 18, 1950, to provide an area tional zonation In ash-flow tuffs, and for continental testing of nuclear devl- studies of secondary mineralization. ces. In January of 1951 testing began The rock sequence at NTS Is composed of with an airdrop Into Frenchman Flat in late Precambrian and Paleozolc rocks which conjunction with Operation Ranger. In were completely deformed by Mesozoic addition to airdrops, above ground testing compressional tectonism. Tertiary and Included surface detonations, tower shots, Quaternary volcanic and clastic rocks and balloon suspensions. Underground overlie the older rocks and were deposited testing began In 1957 and, since 1963, all concurrent with Cenozoic extensional events have been buried In large diameter faulting. The late Miocene ash-flow tuffs drill holes or tunnels. Geologists from and lavas found In this area issued prl- the U. S. Geological Survey mapped much of marily from the Timber Mountain-Oasis the NTS region between 1960 and 1965. Valley caldera complex located In the These maps have formed the basis for western part of NTS. Studies performed In subsequent studies by geologic support conjunction with nuclear testing and groups from Los Alamos National Labora- radioactive waste Isolation have addressed tory, Lawrence Livermore National Labora- many aspects of the geologic history of tory, Sandia National Laboratory, and the NTS which have In turn greatly enhanced USGS. A good geologic understanding of our understanding of the geology of the the stratigraphy, structure, geochemistry, southern Great Basin. and physical properties of the rocks is The editors would like to thank all of essential for adequate containment of the co-authors who contributed to sections underground nuclear tests. Many of the of this guidebook In their areas of exper- recent geologic studies at NTS, particu- tise. Special thanks to Will Carr whose larly In Yucca Flat, Pahute Mesa, and numerous additions and corrections to the Mid-Valley are aimed at understanding roadlog were Incorporated Into the final subsurface geology to help ensure complete draft. W. B. Myers and D. L. Nealey of containment. Since 1978, the massive the USGS reviewed the manuscript. Without ash-flow tuff beds under Yucca Mountain the support of Jack House and Wes Myers of have been Intensively studied to determine Los Alamos National Laboratory, this field their potential as a radioactive waste trip would not have been possible. 1 ANDER & OTHERS Virginia Glanzman expedited the USGS peer Vegas Valley on the southwest, whereas review process and performed editorial several smaller northerly-trending ranges duties. Barbara Hahn typed the manuscript have southerly terminations on the north- and Mary Ann Olson and Luween Smith draft- east side of the valley. The sharp west- ed many of the illustrations. erly bending or "drag" into the Las Vegas Valley shear zone of major northerly ROADLOG structural and topographic trends (indi- DAY 1 cated by ranges on the northeast side of GENERALIZED STRUCTURAL GEOLOGY FROM LAS Las Vegas Valley), and offset of Paleozoic VEGAS TO MERCURY facles markers (Stewart, 1967) and major thrust faults on either. side of the valley The Las Vegas Val ley shear zone, one of (Burchfiel, 1964) Indicates right-lateral the major structural features of the Basin movement along the zone. Studies of and Range physlographic province, Is stratigraphic and structural evidence reflected topographically by the north- indicate an aggregate right-lateral offset west-trending Las Vegas Valley (Fig. 1). of 60-75 km. occurring between about 17 The Spring Mountains, culminating in to 11 m.y. B.P. (Longwell, 1974). The Charleston Peak (3633 m.), parallel Las absolute amount of strike-slip movement FIGURE 1: Southern Nevada region showing principal geographic features, probable offset of Wheeler Pass Thrust and coeval Gass Peak Thrust, and numbered stops on Nevada Test Site Field Trip. 2 NEVADA TEST SITE GEOLOGY along the shear zone cannot be determined, nian age (probably Ironside Dolomite In part due to alluvial cover, but estl- Member of Sultan Limestone). It mates range from 27 to 30 km. (Fleck, rests with apparent unconformity on a 1970). The rest of the offset Is attribu- very thin gray dolomite of Devonlan ted to structural bending or "drag." or possibly Silurian age, which In The area traversed on this field trip turn rests unconformably on gray and lies In a belt of extensive thrust faults brown silty and clayey carbonate of that occur along the east side of the the Pogonip Group of Ordovician age. Cordilleran mlogeocline. These thrust Above the Ironside Dolomite Is lime- faults are of Mesozoic age and occur in stone and dolomite of the Devonian the hinterland of the Sevier orogenic Sultan Limestone. The main ridge Is belt. U.S. Highway 95 follows the valley capped by Monte Cristo Limestone of for about 90 km. from Las Vegas to the Mississippian age. Small outlier vicinity of Mercury, Nevada (Fig. 1). Just north of the end of the main ridge Is composed of the Bird Spring Mileage Formation of Pennsylvanian and Per- 0.0 Las Vegas, Intersection of Interstate mlan age. 15 and U.S. 95. Proceed north on U.S. 95. 16.1 Charleston Park Road - Kyle Canyon turnoff (Nevada State Highway 39). 2.7 Decatur Blvd. overpass. 19.4 Rest area on right ... continue 9.1 Craig Road turnoff. Potosi Mountain straight ahead. A few of the geo- at 8:30 Is capped by Monte Cristo logic features exposed In the next Limestone of Mississippian age. few miles near the Lee Canyon Road Prominent ridge between 8:00 and 9:00 (Nevada State Highway 52) are out- Is capped by Permian Kalbab Lime- lined on Fig. 1. The offset of the stone. Wilson Cliffs between 8:30 Wheeler Pass and Gass Peak thrusts is and 9:30, composed of buff and red commonly cited in support of right- Navajo (Aztec) Sandstone of Triassic lateral movement along the shear and Jurassic age, forms the lower zone. The contrast In rock fades plate overridden by Keystone thrust. and thicknesses on opposite sides of Narrow ridge at 9:30 Is an erosional the valley offer corroborative evi- remnant of Keystone thrust; the ridge dence of strike-slip movement. Is capped by gray Goodsprings Dolo- To the northeast: The rocks of the mite of Cambrian and Ordovician age Sheep Range between 2:00 and 3:00 are overlying red Navajo Sandstone. On the typical thick miogeoclinal sec- La Madre Mountain between 9:30 and tion of eastern Nevada. The two 11:00 are exposed carbonate rocks of prominent black bands at 3:00 are the Cambrian, Ordovician, Silurian(?), lower member of the Ely Springs Devonian, Mississippian, Pennsylva- Dolomite repeated by faulting. nlan, and Permian age. On Sheep Beneath the upper of the two black Range at 1:00 the outcrops are rocks bands Is the light-colored Eureka of Cambrian through Mississippian Quartzite. The Eureka Is underlain age. On Las Vegas Range between 1:00 by brownish-gray Pogonip Group car- and 3:00 most outcrops are the Bird bonates, which in turn are underlain Spring Formation of Pennsylvanian and by the Nopah Formation, the top Permian age. Muddy Mountains at of which has prominent black and 4:00. Sunrise and Frenchman Moun- white stripes. Above the black lower tains between 4:30 and 5:30. member of the Ely Springs Is a unit of light-gray dolomite representing 14.8 View of La Madre Mountain stratigra- the upper member of the Ely Springs phy between 9:00 and 10:00. Lower and lower part of the Silurian. The thin black band Is dolomite of Devo- thin black band is a dark dolomite 3 ANDER 6 OTHERS unit within the Sliurlan section. The grained beds have yielded fossil Devonian rocks above are similar to mollusks and mammals of Pleistocene the Nevada Formation and the Devils age. Gate Limestone of the Test Site. To the southwest: The ridge east 29.5 Lee Canyon turnoff. Nevada 52 on of Lucky Strike Canyon consists of a left--continue straight ahead. At much thinner section than In the 9:00 on skyline Is Charleston Peak, Sheep Range and contains several elevation 11,918 ft. (3612 m.). different lIthofacIes. At 10:00 a Black Ridge at 3:00 Is composed of white streak representing the distal Cambrian and Ordovician strata. end of the Eureka Quartzite may be Desert Range at 2:00 Is composed of seen just below a prominent black Cambrian to Devonian strata. unit, which Is probably equivalent to the Ironside Dolomite Member of the 33.0 Playa of Three Lakes Valley at 2:00. Sultan Limestone (Nevada Formation) PIntwater Range at 1:00 Is composed of Devonian age. A thin light-gray of Cambrian to Devonlan strata. dolomite separates the Eureka and Indian Ridge at 10:30 Is composed of Ironside. This dolomite contains the Cambrian and Ordovician rocks. Ordovician Ely Springs Dolomite and Ridge, between 8:00 and 10:00, Is possibly a thin Silurian section. composed of Bird Spring Formation. The Devils Gate Limestone forms the The Wheeler Pass thrust probably remainder of the ridge above the separates these two ridges. black Ironside (Nevada Formation). The Mississippian Monte Cristo Lime- 34.9 State Correctional Facility, Camp stone forms the north-dipping slope Bonanza (Boy Scouts of America), and of the main ridge and cannot be seen Cold Creek Road on left--continue from here. The well-bedded outcrops straight ahead. at 11:00 north of Lucky Strike Canyon are the Pennsylvanian-Permian BIrd 39.0 Southwest end of Pintwater Range, Spring Formation. Below the Eureka between 1:00 and 3:00, Is composed of at Lucky Strike Canyon, the section Ordovician and Silurlan-Devonlan Is gray and brown silty and clayey rocks. Ridge at 10:00 Consists of carbonate rocks of the Pogonip Group. gray cliffs of Monte Cristo Limestone The black dolomite just above the and alternating brown silty-sandy valley fill at 9:30 Is the upper part limestone and gray limestone of the of the Nopah Formation. Bird Spring Formation. Prominent Fossil Ridge at 4:00 Is composed of high point on skyline ridge, at 9:30, Cambrian and Ordovician rocks. Gass Is Wheeler Peak. Peak thrust (Fig. 1) at 4:30, separ- ates upper plate of Cambrian rocks on 41.0 Light-gray outcrop, at 3:00, Is left from lower plate of Pennsylva- mostly Devonian carbonate rock. Near nian-Permian rocks of the Las Vegas this point, the trend of Las Vegas Range on the right. Valley changes from northwest to west-southwest past Indian Springs, 25.3 Lucky Strike Canyon Road to left. reflecting either a bend In the Las Road to right leads to Corn Creek Vegas Valley shear zone or the pre- Springs Field Station of U.S. Fish sence of a conjugate northeast-trend- and Wildlife Service which manages ing fault. the Desert Game Range. Continue straight ahead. 42.1 Village of Indian Springs. Indian Springs Valley Is at 3:00. White and 26.0 Badland topography at 3:00 developed brown outcrops In distance, at 1:00, on Las Vegas Formation. Near Las are Eureka Quartzite. Dark dolomite Vegas, similar yellowlsh-gray fine- on ridge at 12:30 Is Upper Cambrian 4 WRIEWIM" NEVADA TEST SITE GEOLOGY Nopah Formation. Gray and brown ridge on the skyline. Strata seen gener- outcrops forming prominent ridge ally dip 30' to 40- northwestward and form south of town, 9:00 to 11:00, are the southeast limb of the Spotted Range Bird Spring Formation. syncline. The rocks are displaced by a prominent system of northeast-trending 45.4 Village of Cactus Springs. Prominent faults. White quartzite member of the black and white banded. dolomite on Eureka Just above valley fill at 1:30 Is ridge between 1:00 and 3:00 is upper overlain by black dolomite of the lower part of Nopah Formation. member of the Ely Springs. Ridge on skyline between 12:30 and 2:30 Is South 47.7 Prominent ridge on skyline between Ridge capped by Devils Gate Limestone. 9:00 and 12:00 Is northwest end of Nevada-Devils Gate contact is on skyline Spring Mountains; Wheeler Peak at at 1:30. Prominent black band with brown- 9:30, Mount Stirling at 10:30. ish slope-former below Is the lower part of the Nevada Formation and can best be 49.5 Road to right leads to test well 4-- seen In middle part of range between 2:00 continue straight ahead. Lake beds and 2:30. of the Las Vegas Formation form the yellowish-gray badland topography 58.7 Low ridges In foreground between along highway. These beds marking a 10:30 and 2:30 are Ordovician Ante- significant shoreline of a large lope Valley Limestone. Ridge on lake, continue westward only a few skyline between 11:00 and 1:00 con- more miles where they reach a maximum sist of Eureka Quartzite through altitude of about 1100 m. They are Devils Gate Limestone. continuous from that point back to an altitude of about 800 m. In the Las 59.3 Massive gray cliffs at 3:00 are the Vegas area suggesting a southeasterly Palilseria-bearing limestone In the tilting during the last million years middle part of the Ordovician Ante- of approximately 5 m./km. lope Valley Limestone (lower part of the Aysees Member of the Antelope 52.7 Brown and gray outcrops Immediately Val ley Limestone In the Ranger Moun- north of highway are Pogonip Group. tains). Underneath are brown slopes of the Orthidiella-bearlng silty 55.1 STOP 1. PALEOZOIC UNITS IN THE limestone (Ranger Mountains Member of SPOTTED RANGE. the Antelope Valley Limestone in the Park off highway on right side near Ranger Mountains). sign designating Nye-Clark County line. 59.5 Highway bends to more westerly direc- tion. Hills on skyline between 12:00 Rocks seen to the north In the Spotted and 1:00 are Specter Range. Skull Range are typical thick mlogeosynclinal Mountain In distance at 2:00 is strata similar to those In the Sheep Range composed of sillcic volcanic rocks, section. Visible units Include limestone capped by black basalt flows. Mer- of the Ordovician Pogonip Group, Eureka cury camp at 4:00. Mercury Valley to Quartzite, and Ely Springs Dolomite (see northwest Is the last topographic Table 1); Silurian and Lower Devonian expression of the northwest-trending dolomite; Lower and Middle Devonlan dolo- Las Vegas Valley or La Madre shear mite and quartzite of the Nevada Forma- zone. Northeast-striking structures, tion, and Middle to Upper Devonian Devils Including thrusts In the Specter Gate Limestone (includes some dolomite and Range and Spotted Range can be corre- quartzite). Uppermost Devonian and Lower lated across Mercury Valley with to Upper Mississippian rocks cannot be little or no offset. No significant seen from here, but are present In an northwest-striking faulting Is pre- overturned syncline on the far side of the sent In Plio-Plelstocene deposits of 5 - - ANDER & OTHERS TABLE 1 PRE-CENOZOIC ROCKS EXPOSED IN AND NEAR YUCCA FLAT, NEVADA TEST SITE (modified from Qrkcild. 1982) Approximate Thickness Age Formation m Dominant Lithology (m) Upper carbonate Permian (?) and Penn syl vani an Tlppipah Limestone 1100 limestone (1100) Mississippian and argillite. Upper clastic Devoni an Eleana Formation 2320 quartzite (2320) Devoni an Devils Gate Limestone 420 l imestone Nevada Formation 465 dolomite Devonian and Sil uri an Dolomite of Spotted Range 430 dolomite Ordovician Ely Springs Dolomite 93 dolomite Lower carbonate Eureka- Quartzite 104 quartzite (4700) Antelope Valley Limestone 466 limestone Ninemnile Formation 102 si 1tstone Goodwin Limestone 290 limestone Nopah Formation 565 limestone, Cambrian dolomite Dunderberg Shale Member 49 shale Bonanza King Formation 1400 limestone, dolomite Carrara Formation 305 limestone 305 sil tstone Zabriskie Quartzite 67 quartzite Wood Canyon Formation 695 quartzite, Lower clastic siltstone (2900) Stirling Quartzite 915 quartzite Precambri an Johnnie Formation 915 quartzite, (base not exposed) limestone, dolomite TOTAL THICKNESS 11,000 + Mercury Valley. Bonanza King down against uppermost Precambrian and lower Cambrian Wood 60.8 Mercury interchange. (Mercury camp Canyon Formation. 4:00) . 68.5 On r I ght, contact between Upper 12 well 63.1 Army site on right. Precambrian Stirl ing Quartzite and Wood Canyon Format Ion. 63.7 Right side of road Is southeast end of the Specter Range, left side Is 69.1 On left Miocene-Pliocene gravels northwest end of Spring Mountains. conta I n at the ir base ash-fa I I tu f f Rocks In canyon alongside highway are layers correlative with those at the largely Bonanza King Formation of base of the Paintbrush Tuff (Table Cambrian age. 2), whose source Is near the western edge of NTS, 56 km. to the northwest. 66.6 Telephone relay station on right. Unconformably beneath the ash beds Bonanza King Formation at 3:00, Nopah are steeply tiIted early Miocene Formation at 9:00. tuffaceous sediments. 67.5 On right, large fault brings Cambrian 69.8 Intersection of U.S. 95 and road to 6 -u NEVADA TEST SITE GEOLOGY Pahrump. On skyline at 11:00 are the Funeral Mountains. 70.8 Light gray hills at 3:00 are highly A WAXSMPRlN faulted Antelope Valley Limestone. 51171t 74.8 Low pass through Silurlan Lone Moun- tain Dolomite on right and Nopah Formation on left. 75.3 To right, exposure of Ely Springs at 2:30-3:30 (dark band), underlain by Eureka Quartzlte Just above valley fill and overlain by undifferentiated- Silurlan dolomite. Amargosa Desert 10- 10M IL to left. 6 ,; vawurMMvS 79.3 Low hills of Stirling quartzlte to Vr-i" cq~nAIaan OFTIABOR -¶I1'I PtmPWf Y OFiiuim MO NJTAIN MOLi4A1N.ULEW~CANYoN RESUNOENTDOME. right and left of highway. At 1:00 CALOERACOMftM~ low hills of Carrara and Wood Canyon OASMEWIH!R PMENffL. Formations. FIGURE 2: Nevada Test Site region showing caldera outlines, known and inferred. 80.3 Bonanza King Formation crops out to right. 80.8 Bonanza King -Formation exposures on left. 84.9 Tunnels for MX experiments In Little Skull Mountain visible at 3:00. 82.0 Rock Valley Wash. 87.1 Village of Lathrop Wells. Highway to 83.0 Fresh water limestone beds In low left goes to Death Valley Junction, hills on 'right and left. Equivalent California, and to Death Valley via beds have been dated at 29.3 + 0.9 Furnace Creek Wash. At 2:00-2:30 Is m.y. In Frenchman Flat area. Hills Yucca Mountain; on skyline behind at 9:00 are composed of Bonanza King Yucca Mountain Is Pinnacles Ridge, Formation. which forms the south rim of Timber Mountain caldera (Fig. 2), discussed 83.5 Lathrop Wells Paleozolc section In detail on second day of field (Sargent, McKay, and Burchfiel, trip. Also visible Is Fortymile Wash 1970), In Striped Hills at 2:00 to and the varicolored volcanic rocks of 3:00, begins In Wood Canyon Formation Callco Hills. Range to left In dis- Just above the sand fan. Essentially tance is Funeral Mountains, which complete Cambrian section Is vertical forms the east side of Death Valley. to slightly overturned. In ascending order Wood Canyon Formation, Zabris- 90.2 Fortymile Wash crosses U.S. 95. To kle Quartzite, Carrara, Bonanza King left at 11:00 Is Big Dune composed of and Nopah Formations. The Bishop ash eollan sand. occurs In sandy alluvium forming large fan on south slope of hills at 92.2 Southernmost end of Yucca Mountain 3:00. The Bishop ash erupted from Just north of U.S. 95 on right. Long Valley caldera, approximately Outcrops are Miocene Paintbrush and 235 km. to the northwest about Crater Flat Tuffs (see Table 2) 730,000 yrs. ago. repeated by northeast-striking faults. 7 ANDER & OTHERS TABLE 2 PRINCIPAL CENOZOIC VOLCANIC AND SEDIMENTARY UNITS (modified from Orkild. 1942 and Carr. Byers. and Orkild. In press) Approximate FORMATION, Member Inferred Volcanic Center General Composition Age (m.y.) YOUNGERBASALTS WllMEROUS Basalt (hawalite) 0.3-7 THIRSTY CANYONTUFF BLACK MOUNTAIN CALDERA Trachytic soda rhyolite 7-9 RHrOLITE OF SIOSNOlE MOUNTAIN SHOSHONEM(UNTAIN HIgh-1ilica rhyol1t. BASALT OF SKULL MOUNTAIN, EGAO JACKASS FLAT(?) Quartz-bearing basaltic andesite 10 TIMBER MOUNTAIN TUFF TIMBER MOUNTAIN CALDERA Rhyolite to quartz latite 10-12 IntraC4ldera ash-flow tufts Amonia Tanks Member Rainier Mesa Member PAINTBRUSH TUFF CLAIM CANYONCALDERA Rhyolite to quartz latite 12-13 Intracaldera ash-flow tufts Tiva Canyon Member Yucca Mountain Member Pak Canyon Member Topopah Spring Member WdAHMONIEAND SALVER FORMATIONS WAsOIE-SALYER CENTER Dacitic tufts and lavas 13-13.5 CRATERFLAT TUFF (coeval with tufts CRATERFLAT(?). Calderas Rhyolite 13.5-14 of Area 20) buried under basalt and Prow Pass Member alluvium Bullfrog member Tram Member STOCKADEWASH TUFF (coeval with Crater SILENT CANYONCALDERA Rhyol ite 14 Flat Tuff) BELTED RANGETUFF SILENT CANYONCALDERA Peralkaline Rhyolite 14-15 Grouse Canyon Member Tub Spring Member TUFF OF YUCCAFLAT UNCERTAIN Rhyol ite i5 REDROCKVALLEY TUFF UNCERTAIN Rhyol Ite 15 FRACTION TUFF CATHEDRAL RIDGE CALDERA Rhyolite 17 ROCKSOF PAYITS SPRING (underlies DISPERSED Tuffaceous sediments 14-? Crater Flat Tuftf) HORSESPRING FORMATION DISPERSED Mostly sediments 30 93.2 STOP 2. YOUNG BASALT CONES AND FLOWS 3.7-M.Y. CYCLE (Pb) (Fig. 3). Rocks of the oldest cycle consist of deeply dissected cones and flows with The Crater Flat area (Fig. 1) contains locally exposed feeder dikes. They occur over 15 small basaltic volcanic centers In the central and southeastern part of composed of cinder cones and associated Crater Flat (Fig. 3). lava flows. Only the youngest center Is visible at this stop. The distribution, 1.2-M.Y. CYCLE (Qb) petrology, and tectonic setting of the Basaltic rocks of this cycle consist of basalts has been described by Crowe and cinder cones and lava flows located along Carr (1980), Vaniman and Crowe (1981), a northeast, slightly arcuate trend near Yaniman and others (1982), Crowe and the center of Crater Flat (Fig. 3). From others (1982), and Crowe and others (1983a northeast to southwest, the major centers and 1983b). The rocks are divided into In this cycle Include unnamed cone, Black, three eruptive cycles based on geologic Red, and Little Cones. field relations, potassium-argon ages, and magnetic polarity determinations. The 300,000 YR. CYCLE (Qb) K-Ar ages listed below were done by R. J. The youngest cycle Is marked by essen- Fleck (written commun., 1979) and R. F. tially undissected cones and flows of the Marvin (written commun., 1980). Lathrop Wells center at Stop 2. The 300,000 yr. basalt cycle at the 8 - U ~ NEVADA TEST SITE GEOLOGY Lathrop Wells volcanic center (Stop 2) Includes a large cinder cone with two small satellite cones which overlie and % t / '22@ *li n WAR AWR are flanked to the east by aa flows (Fig. Pr sr 6 M t O/LIErATERNARV BASAL?LAVA 4). Calculated magma volume Is about 0.06 J ftPLOCE BASALTLAVA km3. The satellite cones are overlapped by deposits of the main cone. The large I~~~lwII cone, referred to as the Lathrop Wells t X / S 27 n | 8 , 1 ~~~PRlocLASTIcDEPOSITS cone, has a helght/width ratio of 0.23. ¶ 0$ / \tg I0 MPAUOOCROCK Scattered pyroclastic deposits from the Lathrop Wells vent are found for a dIs- S }#e e~~~~~~i =>V^5UAS.SEPE~NS tance of more than 4 km. to the northwest. W46'~~~~~~~~~~~~~ This alignment of pyroclastic deposits Indicates a strong and consistent wind w g C :3 ~~~~~~~PAQ.ICSEP10TN flow from the southeast during the erup- tion. The cone appears unmodified by erosion except for minor slumping of steep cone slopes. Two aa flows vented at SASALTS several sites along the east flank of the FIGURE 3: Southern Crater Flat area Lathrop Wells cone. Flow vents are marked showing basalt centers and Stops 2 and 3 by arcuate spatter ridges extending east (modified from Crowe and Carr, 1980). and southeast of the cone. The lavas have unmodified flow margins and rubbly flow surfaces consistent with their young age. are also present though poorly exposed. They are locally covered by loess and The center Is located on a regional north- eollan sands. The probable oldest depos- east-trending structural lineament marking its of the Lathrop Wells cone are well- the western edge of the Spotted Range-Mine bedded pyroclastic (base) surge deposits Mountain northeast-trending structural (Fig. 5) that are exposed only on the zone (Figs. 3 and 6); faults west of this northwest side of the cone where they lineament have a more northerly trend. It overlap a topographic ridge upheld by Is suggested that the strike of the faults welded tuff. They probably underlie the influenced the location of the center; scoria deposits of the cone and thus that Is, the eruptions were fed from dikes record an episode of phreatomagmatIc whose trends were controlled by the re- activity during the early eruptive stages gional stress field, I.e. least compres- of the center. sive stress direction. The ages of the Quaternary alluvial The basalts of the Lathrop Wells center deposits are consistent with ages on the are sparsely porphyritic wIth olivine as basalt. Before eruptions, alluvium of the major phenocryst phase (3 modal per- middle Pleistocene age locally developed a cent). They differ from the 1.2 m.y. old dense K horizon that gave a uranfum series basalts by having a slightly greater age of about 345,000 yrs. (Fig. 5). The olivine content and a greater amount of pyroclastic material locally became Incor- unaltered basalt glass. Also the cores of porated in late Pleistocene alluvium (Fig. olivine phenocrysts are slightly more for- 5) and a loesslal silt deposit accumulated steritic (Fo 0 ) than olivines of the on the cinder cone and regionally on the 1.2-m.y. cyc e o077 7 ), as determined by Q2 alluvium prior to about 25,000 yrs. probe. Groundmass phases also Include ago. plagioclase (zoned from An to more alka- The structural controls for the loca- line compositions) and minor amounts of tion of the center are not obvious. The olivine, pyroxene, and Iron-titanium cone summit crater, and the satellite oxides plus Interstitial glass. Textures cones are aligned northwesterly, probably of the basalts of the Lathrop Wells center due to northwest-trending structural are hyalopilltic to pilotaxitic. A de- control. Faults striking north-northeast talled discussion of the mineralogy and 9 b6 ANDER & OTHERS 'GEOLOGIC CONTACT GRADATIONAL CINDER CONE BOUNDARY <, SPATTER RIDGE Ova LAVA FLOW SOURCE AND FLOW DIRECTION -~ Obis C"I'4 STRIKE AND DIP OF CINDER CONE BEDDING Oci QUATERNARY VENT FACIES 0cta QUATERNARY SCORIA DEPOSITS Oc2 QUATERNARY VENT FACIES. OLDER DEPOSITS Cpu QUATERNARY PYROCLASTIC SURGE DEPOSITS 1ba X QUATERNARY LAVA FLOWS (EQUIVALENT AGE) ' Tt TERTIARY TUFF (UNDMDED) 0 1.0 l. . KM FIGURE 4: Geologic map of Lathrop Wells volcanic center (Stop 2). geochemistry of the Lathrop Wells center This section from base upward consists of: Is found In Vaniman and Crowe (1981) and (1) vitric ash-fall tuffs overlain by (2) Vaniman and others (1982). a boulder debris flow (yellowish-green Lavas of the Lathrop Wells center have layers near base of hill), (3) Bullfrog been dated at about 300,000 yrs., consis- Member (dark vitrophyre near base) and tent with the lack of erosional modifica- Prow Pass Member of the Crater Flat Tuff, tion of both cones and flows. The basalts and (4) Topopah Spring and Tiva Canyon are normally magnetized and thus assigned Members of the Paintbrush Tuff (on sky- to the Brunhes Normal Magnetic Epoch. The line). This is the only known section three K-A dates are 300,000 yrs. for where the Crater Flat Tuff Is vitric and agglutinate In the summit crater, 290,000 unaltered, although the Tram Member, the yrs. for the lava, and 230,000 yrs. on a oldest unit, Is missing here. bomb (Fig. 5) collected near the base of The Crater Flat Tuff Is a sequence of the cinder cone. We believe the age on three compositionally similar calcalkalIne the bomb Is probably the least reliable rhyolltic ash-flow tuffs characterized by age because of Its discordance with the subequal modal plagloclase, sanidine, and older ages, which are In close agreement. quartz with minor blotite and hornblende or orthopyroxene (Byers and others, 1976b; 95.6 STOP 3. CRATER FLAT TUFF. Byers and others, 1983; Carr and others, Miocene volcanic units and type 1984, In press). Four K-Ar dates of 14.1 section of the Crater Flat Tuff (Fig. to 12.9 m.y., averaging 13.5 m.y., were 6). Stop at Amargosa Farm Area sign obtained on blotites from specimens In the on right side of road. Hike to hills basal vitrophyre of the Bullfrog Member about 0.5 ml. to north. (Marvin and others, 1970, their Table 2). The source areas for the Crater Flat Tuff 10 NEVADA TEST SITE GEOLOGY 300,000 yrs (agglutinate in crater) EAST WEST 25,000 yrs 290,000 yrs 0 0.5 I I KMf 345,000 yrs Qs - SAND SHEEF .- t - HOLOCENE ALLWIUM pi,$R Go - EOUAN SAND DUNES 01 - LATE HOLOCENE LOESS b - BASALT LAVA . - BASALT CINDER PYROCLASTIC SURGE INTERMEDIATE AGE PLEISTOCENE ALLUVIUM TIMBER MOUNTAIN AND PAINTBRUSH TUFFS FIGURE 5: Sketch of geologic relations at Lathrop Wells volcanic center (Stop 2). are obscured by later volcanism, tecto- about 100 m. thick. The base of the nIsm, and alluviation. Carr (1982; Carr member consists of nonwelded, vitric ash and others, 1984, In press) suggests that flows. These grade upward Into a vitro- the Tram Member was erupted from a caul- phyre about 6 m. thick from which the K-Ar dron partly buried by late Tertiary allu- age samples were taken. The thick Inter- vium In the northern part of Crater Flat, ior of the member Is moderately welded and and that the overlying Bullfrog and Prow thoroughly devitrifled. It contains rare Pass Members were erupted from a buried to sparse xenoliths, a few of which are cauldron In central Crater Flat (Fig. 2). greenish aphyric welded tuff, which may be Warren (1983a, 1983b) has recently corre- peralkaline Grouse Canyon. The uppermost lated the Bullfrog and Prow Pass Members portion of the Bullfrog Member Is partial- with parts of the Area 20 Tuff beneath ly welded vitric tuff. Pahute Mesa. Lenticular masses of monolithologic Although the basal Tram Member of the breccia of welded tuff rest on an Irregu- Crater Flat Tuff ts missing here, the lar surface on the upper part of the Bullfrog Member Is underlain by a thick Bullfrog Member. The monolithologic sequence of bedded air-fall tuffs and breccta Is poorly sorted and consists of reworked volcaniclastic sediments. An clasts of welded Bullfrog Member as much extensive deposit within the bedded tuffs as a meter In diameter. contains large clasts of the Tram Member A thin aerfalt tuff less than a meter and densely welded peralkaline Grouse thick marks the base of the Prow Pass Canyon Member of Belted Range Tuff. The Member. The Prow Pass Is a simple cooling Bullfrog Member, outside the cauldron, at unit less than 50 m. thick, having a this location Is a simple cooling unit nonwelded vitric basal zone, a partially 1I ANDER & OTHERS EXPLANATION APPROX. AGE, M.Y CINDERS (031 BASALT LAVA 0L TIMBER MOUNTAIN TUFF (11.23 PAINTBRUSH TUFF 112.81 Tm CRATER FLAT TUFF (13.51 TUFF AND SEDIMENTARY ROCKS --. - - FAULT. BAR AND BALL ON DOWNTHROWN SIDE FIGURE 6: Generalized geologic map of type section area of Crater Flat Tuff (Stop 3). welded, devitrifled Interior; and a non- 109.9 At approximately 3:00 view Little welded, vitric upper zone. Skull Mountain, capped by Miocene The Prow Pass Is overlain by several (approximately 10 m.y. old; R. F. meters of bedded tuff and by the Topopah Marvin, written commun., 1980) Spring and Tiva Canyon Members of the basalt of Skull Mountain, underlain Paintbrush Tuff. by faulted Miocene Topopah Spring After stop, turn around and return east Member of the Paintbrush Tuff and on U.S. 95. tuffs of the Wahmonle Formation. Low hills at foot of mountain con- 103.9 Turn left on road to Lathrop Wells tain outcrops of the Tram and Bull- guard gate of the Nevada Test Site frog Members of the Crater Flat (NTS). Tuff. Busted Butte at 10:00 is a complete section of the Topopah 105.8 Entrance to NTS through Lathrop Spring Member overlain by Tiva Wells guard gate. Badge check. Canyon Member of the Paintbrush Tuff. Low, white water tank Is at 12 NEVADA TEST SITE GEOLOGY edge of Fortymile Well J-12 at the phy and generalized geology on Fig. Wash. Long rIdge on skylIne to 7 to Stop 4. northwest Is Yucca Mountain. 128.1 Round southern end of Fran Ridge. 113.8 Low hills at 10:00 are Topopah To south at 9:00 Is Busted Butte Spring Member capped by 9.6 m.y. composed of Paintbrush Tuff cut by basalt (R. F. Marvin, written com- a narrow structural slice containing mun., 1980) of EMAD (Engine Mainte- parts of the entire Tiva Canyon nance and Disassembly). Member. Dips range from steeply westward to overturned wIthin a 100 115.2 North side of Skull Mountain at m. wide zone. On the right are 1:30. From top to bottom Is basalt exposures of lithophysal cavities of Skull Mountain, Rainier Mesa and north-northwest-striking frac- Member of Timber Mountain Tuff, tures In Topopah Spring Member In Topopah Spring Member of Paintbrush outcrops along wash. Tuff, and Wahmonle lavas. 128.4 On the skyline at 10:00 is Yucca 117.4 Turn left onto road next to NRDA Crest, at 12:30 Boundary Ridge, at facility, originally Nuclear Rocket 2:00 Bow Ridge, at 2:45 P-1 Hill, Development Station, now called and at 3:30 Fran Ridge, all exposing Nevada Research and Development Paintbrush sequence. Ridges are Area. created by west-dipping major normal faults on west side of each ridge. 119.0 On skyline at 12:00 Shoshone Moun- Strata underlying ridges dip east- tain Is capped by 8.9 m.y. old ward; major normal faults are accom- rhyolite lavas (R. F. Marvin, writ- panied by highly brecclated west- ten commun., 1980). dipping strata. 119.5 Turn left and proceed west toward 130.0 To right along Boundary Ridge, a 20- Yucca Mountain. angular unconformity exists between 11.3 m.y. old Rainier Mesa Member 120.1 EMAD facility to left. Originally and the underlying 12.6 m.y. old used for nuclear rocket engine Tiva Canyon Member (Marvin and maintenance, now operated by West- others, 1970). Rainier Mesa Member inghouse for handling and temporary laps across major faults with only storage of nuclear waste. minor displacement, If any, of the Rainier Mesa. 120.7 Rocket assembly facility at 3:00, one of several built In conjunction 130.6 Turn left toward Yucca Crest. On with NRDS In 1960's. either side are a series of west- dipping normal faults that displace t23.7 Busted Butte at 11:00. the caprock of Tiva Canyon Member, repeating the section. At 12:00 125.2 Road to water Well J-13. Fran Ridge approaching a 20 to 30' dip slope; In foreground to west Is composed of this contrasts with Yucca Crest that Topopah Spring Member, overlain by dips at only 5- to 7-. light-colored bedded tuff and Tiva Canyon Member. 130.8 STOP 4. YUCCA MOUNTAIN. Park bus at driIt hole WT-1 site at 125.4 Crossing Fortymile Wash. mouth of Abandoned Wash. Hike west about 1.5 km. to road at top of 125.9 Turn left at sign for Nevada Nuclear Yucca Mountain; examine fault pat- Waste Storage Investigations INNWSI) terns and compositional and cooling drill hole USW G-3. Follow geogra- zonations In the Tiva Canyon Member. 13 - ^ ANDER & OTHERS GENERALUZEI GEOLOGIC STRIP MAP ACROSS YUCCA MOUNTAIN r1a0UW *I o I*_ GEOLOGIC SECTION I EXPLANATION OUAITRMAVY =0 MI4*K'WdSCO.LL44* '-%Kr O4W OW=C 31Cr** L0.6 DED "IqN MM"WFSW IS W.TAPOaATtOMM7 Tr McMfO., *.. -.CTIS "LA"N MOTNW 0r0 Arn.T v.511s 5,r SOOT O.94O "P* WiSSIo I" G&OWST"S F CIASISO -(Al 1IMh.MOMAUTPA notm om mm0 010 s110 4 TO noccA cmr swwG.2Q of. OLm ocno I L .T ON TOeOPAMS'.ft MSEU FIGURE 7: Geology of a part of the Yucca Mountain area (Stop 4). Intervening blocks, graben-l Ike features The generalized map and accompanying (Fig. 7) suggest a geometric control by detailed geologic section (Fig. 7) show the shape of major normal faults. The this part of Yucca Mountain to consist of attitude of major faults decreases from a series of north-trending, eastward- the average of 70- at the surface to 60 tilted structural blocks, repeated by at depth as suggested by some drill holes. west-dipping normal faults. West-dipping The development of tension gashes would strata along these normal faults are evolve Into rotated normal faults and interpreted as drag zones. On Yucca Crest related grabens with greater degrees of strata dip eastward at 5 to 7-; however, extension. On Busted Butte, rotated fault to the east, strata also dip eastward, but slices extend to depths greater than 200 commonly from 20' to vertical. Coincident m.; If this geometry is typical, then any with the dips greater than 20 are abun- decrease in dip on the major normal faults dant west-southwest-dipping faults with 1 must occur at greater depths. m. to 5 m. of vertical displacement. From the top of Yucca Mountain, you can These faults and related fractures are see the late Precambrian and Paleozolc nearly perpendicular to tuff foliations, rocks of Bare Mountain and P1lo-Plelsto- suggesting rotation. In addition to cene cinder cones and basalt lavas In required rotation of the fault planes and Crater Flat. The steep east-facing front 14 NEVADA TEST SITE GEOLOGY Fault scarp in Quaternary deposits Lineament or covered :.:: portion of fault HQ)~~~~4 Fault scarpment with possible RV-2 minor Holocene displacement STOP a V O g ITenTrtay-Guaternary Alluvium eTv FTertlary volcanic rocks = Paleozoic rocs O, .u . *. .0e' i 0 Tv N o I MILE 4 o 1 KM SPECTER RANGE FIGURE 8: Sketch map of Quaternary faults In Rock Valley (Stop 6). of Bare Mountain may be a major bounding Member as candidate host for nuclear waste fault that formed during subsidence of the repository. Turn around and retrace route caldera complex (Fig. 2) that Is the back to NRDA facility. probable source of the Crater Flat Tuff. 157.3 Turn right at NRDA camp facilities. LUNCH. Hike back down to bus. Turn around and retrace route to turn off for 158.7 Proceed through Intersection; BREN NNWSI drill hole G-3. (Bare Reactor Experiment-Nevada) Tower (height 480 m.) at 10:00. 139.3 Turn left on main paved road at sign "Underground Storage, Waste (USW) 162.7 At the divide Skull Mountain Is drill-hole USW-G4." separated from Little Skull Mountain to southwest by northeast-striking 145.0 STOP 5. POSSIBLE NUCLEAR WASTE high-angle fault system, down to the REPOSITORY. northwest. There Is also probably a (Depending on time, this stop may be strong left-lateral strike-slIp cancelled). component. Exploratory Hole USW-G4 for proposed 163.6 Light-colored massive tuff at 3:00 exploratory shaft to test Topopah Spring Is nonwelded Bullfrog Member of the I I 15 ANDER & OTHERS Cobbleood ould good02 EXPLANATION 0,srurbed zone; Modern rooteots and *000* Soil colicft Root lobes Cal-het tfilled root Ntese. Stloghs duo to eaOa Ornentrtion - --- Contact, domted .here *q906 at olcertaint AGES 0 2 3 4 Sampls 97: 2 Th/ U age of > 5,0O yrs. Fault at trOctultO, deote.d where uqcorto.0 Samoll, 82- Sample 307: u-Trend of 38,000 ± 1O.OOOyrs. 0s otolocoe otlu0,uog Sample RV-IU: U-Trend age of 31.000t5,000yrs ItelrmedOte altuguom(NlddtO oJ Loop I' oistOCORIP) 02 Sample RV-1L: U- Trend age of 310,000 30.000yrt. oTa Older atll.jueo(PIi@lceC@ t71and Early PleistocOOOJ Atigillic B some. I U- Trend sample0 location Nort h Fast Waif1 Trench f South L3 SofasBottomof Bured offlce S to Ctresc B zonetoa 2 O's0 tur* Feet 1 2 3 FIGURE 9: ProfIles of trenches on Rock Valley fault zone (Stop 6). Crater Flat Tuff. tion of the fault scarps and trenches Is shown on Fig. 8. The stop Is at trench 164.7 Specter Range at 12:00 composed of RV-2. The trend (RV-2, Fig. 9) Is cut lower Paleozolc carbonate rocks. across the scarp at a point where it Is only about 1.5 m. high and has a maximum 166.6 Road crosses southeast-facing eroded slope angle of about 6-. Along most of fault scarp In alluvium; fault Is the scarp, farther northeast, the height part of Rock Valley system of north- of the scarp, accentuated somewhat by east-striking Quaternary faults erosion, Is as much as 4 m. and the slope (location B, Fig. 8). angle is about 8'. In several drainages the scarp has been completely breached and 169.6 Turn off at 5310 Road. removed by erosion east and west of the trench location. 173.0 STOP 6. ROCK VALLEY FAULT SYSTEM. The trench Is cut mainly In Q2 allu- vium, whose age is generally between about Trench RV-2 on strand of Rock Valley fault 35,000 and 750,000 yrs. (Hoover and oth- system. In 1978, two trenches were dug ers, 1981). U-trend dates suggest two across one of the most prominent Quater- ages of Q2 are present (Fig. 9) In the nary strands of the Rock Valley fault trench. At several places In the bottom system, a part of a major northeast-strik- of the trench are small exposures of ing, selsmically active, structural zone probable QTa alluvium; on the downthrown In the southeastern NTS area. The loca- (north) side of the fault QTa has an 16 * NEVADA TEST SITE GEOLOGY argiliIc zone preserved, but on the There seems to be no surface evidence upthrown side the B zone Is missing, of the younger 0.3 - 0.6 m. offset along presumably as a result of erosion, and the old scarp and no Holocene alluvium Is parts of a K zone are exposed between obviously affected, so It Is reasonable to faults on the upthrown side. A thin conclude that the event was probably laminar carbonate zone, a probable K pre-Holocene. horizon, occurs within the Q2 alluvium; It At location C (Fig. 8), a branch of the Is overlain by a light orange-brown, trenched fault extends east-northeast slightly clayey B zone. At the north end across QTa; It has about 0.5 m. of dis- of the trench Is a thin deposit of Q1 placement, but the scarp Is very subdued. (Holocene) alluvium. QTa with a thin At the east end of this fault It passes veneer of Q2 forms the upthrown surface Into Miocene volcanic rocks where It Is south of the trench. Ages obtained here only possible to limit Its amount of total and In trench RV-1 by uranium-series displacement to less than 3 m. methods are by B. J. Szabo and J. N. At location D (Fig. 8), a defInite Rosholt of the USGS, and are listed on lineament visible on aerial photos occurs Fig. 9. U-trend determinations from the In Holocene (Q1) alluvium; the llneament lower part of Q2 are about 300,000 yrs.; Is a westward extension of a fault In dates from the upper part of Q2 are about alluvium that parallels the trenched 35,000 years. Two samples of the laminar fault. However, as mentioned at location carbonate K horizon gave ages of greater A, calcrete In a fracture suggests no than 5,000 yrs. To the west, on a paral- major movement on this fault after about lel fault at location A (FIg. 8), undis- 20,000 yrs. ago. The lineament at loca- turbed calcrete filling a fracture adja- tion D (Fig. 8) cannot be seen on the cent to the fault gave a uranium-series ground and It could be only a subtle brush age of greater than 20,000 yrs., suggest- line where bushes have grown preferential- ing no reopening of the fracture and ly by sinking their roots Into the fault probably no major movement on the adjacent zone through a thin cover of Holocene fault after 20,000 yrs. ago. alluvium. Because the evidence that the At least two faulting events appear to latest event was pre-Holocene is not be recorded on the fault zone exposed In compelling, however, It is not possible to trench RV-2. The older event, which rule out an Important earthquake of Holo- produced a small graben In QTa (Fig. ?), cene age on the Rock Valley fault system. and was probably responsible for the preserved 1.5 + m. high scarp, must have 176.9 Turn left onto Jackass Flats High- occurred after deposition of QTa and way. subsequent soil formation, which probably places It after 1 m.y. ago;. the minimum 183.6 Junction of Jackass Flats Highway age of the event Is constrained only by and road to Camp Desert Rock Air- the less disturbed youngest Q2 alluvium port. and tts soil, or before (at least) 35,000 yrs. ago. Fault strands that offset the 188.0 STOP 7. MERCURY, NEVADA. QTa extend upward into Q2 and vague stra- tificatlon In the older Q2 suggests that USGS Core Library. (Depending on time It was not deposited across the scarps In schedule, the presentations planned for QTa, but faulted along with it. There- this stop may be given In the evening fore, It Is suggested that the older event after dinner at the Mercury Steakhouse). occurred after about 300,000 yrs. ago. The younger event, shown by 0.3 - 0.6 INTRODUCTION m. offsets of the Q2 soil and Its laminar K horizon can only be dated as younger The Geologic Data Center and Core Library, than about 35,000 years, the approximate maintained by the U.S. Geological Survey minimum age of the younger Q2 (Hoover and (USGS) at the Nevada Test Site, is a others, 1981). depository for systematic processing, 17 ANDER & OTHERS cataloguing, and storage of drill-bit cildes. Examples of both types of work cuttings, drill core, and other rock are described below. Petrographic ex- samples from the NTS and other test areas. hibitsof various types of rock samples The facility maintains reference files of will be available for Inspection at the reports, maps, aerial photographs, down- -Core Library. hole video tapes of selected drill holes, and geophysical logs for NTS and other PRIMARY MINERALS test areas, and waste management drill holes. Handling of water samples for both One major project undertaken by Los Alamos chemical and radiological analyses is National Laboratory has been to analyze expedited In a hydrologic-chemical labora- phenocryst minerals and whole rocks to tory. The facility serves as field head- model the entire late Tertiary volcanic quarters for USGS geologists, hydrolo- sequence at NTS. Recent work has allowed gists, and geophysicists, and serves as a accurate correlation of Individual petro- work area for earth scientists In support logic units, generally corresponding to of weapons testing and waste management member rank, and entire petrologic suites projects of the Department of Energy (i.e. Timber Mountain or Paintbrush (DOE). Tuffs), which occur in two widely separa- The Data Center complex comprises the ted locations - Yucca Mountain and Pahute three conjoined buildings at Stop 7, and Mesa (Warren, 1983a, 1983b). Spatial three other buildings. To date, storage distribution patterns of correlative has been provided for about 760,000 m. of petrologic units define the Timber Moun- drill-hole samples stored In about 50,000 tain-Oasis Valley magmatic system as the boxes. Drill-hole samples Include drill- primary source for the entire volcanic bit cuttings, nominally collected each 3 package. This fact, along with supporting m. of drIlled interval, borehole sidewall geochemical data, indicates that the NTS samples, percussion-gun borehole sidewall volcanic pile Is Indeed the effusive samples, and conventional diamond-bit core product of a single, large, evolving samples ranging In diameter from about rhyolitic magma body (e.g. Hildreth, 1981) 2-1/2 to as much as 20 cm. Samples repre- that was located beneath the present sent rocks penetrated In vertical, horl- expression of the Timber Mountain caldera. zontal, or oblique-angle drill holes, The model Inferred for the sequence In- which average about 550 m. In length, but volves two processes: Injections of new range from about 60 m. to 4,171.5 m. In magma and heat from below and continuing depth and from about 2 m. to 1,124.7 m. In magmatic differentiation. Successive horizontal penetration. Detailed records, petrologic suites exhibit dramatically comprising thousands of data cards, are different mafic mineral chemistry, which maintained on all samples, Including date Is theorized to be the result of Influxes received at the Library, source, and final of magma (usually basaltic) from depth. storage or disposition. Individual petrologic units within the petrologic suites each show a distinctive USE OF ROCK SAMPLES feldspar chemistry which probably Is caused by differences In pressure, tem- Continuous core, sidewall samples, and perature, and compositional regimes within rock cuttings stored at the Core Library the evolving magma body. Good evidence have been used to resolve geologic prob- for the probable cause of chemical changes lems encountered by programs such as between successive petrologic units can be nuclear test containment and radioactive seen In the transitional bedded tuff unit waste storage. Primary minerals and whole (Tmpt.), which lies between the Timber rocks are analyzed to help correlate Mountain and Paintbrush Tuffs and shows volcanic units found at the Test Site, and petrochemistry characteristic of both secondary (diagenetic) minerals have been volcanic suites. It contains quartz studied Intensively for their capability phenocrysts along with a substantial Inhibiting migration of radioactive nu- amount of forsteritic olivine (Fo76 8o). 18 NEVADA TEST SITE GEOLOGY Several observations Indicate that this nonequllibrIum mixture Is caused by the mixing of rhyolitic and basaltic liquids. At one drill site, an olivine-bearing alkali basalt layer was cored between the Tmpt unit and the top of the Paintbrush Tuff. Also, basalt fragments are present In all samples of Tmpt. A particularly large basalt fragment seen In thin section shows a highly reacted and poorly defined boundary with the tuff matrix which sug- gests that the basalt was still liquid when mixed with the tuff. Finally, oIl- vine xenocrysts observed In the inclusions or in Tmpt hove altered rims presumably due to reaction with a rhyolitic magma having a high silica activity. These features are all Illustrated In core, thin sections, chemical diagrams, and photomi- crographs displayed at this stop. SECONDARY MINERALS - ZEOLITIZATION AT YUCCA MOUNTAIN Many of the glassy volcaniclastic rocks at NTS have been zeolitized during low-temp- erature diagenests. Typical hydrous FIGURE 10: Lithology of Topopah Spring mineral products of glass alteration are vitrophyre (Stop 7), generalized from clinoptllolite, mordenite, and, at greater drill holes on Yucca Mountain. depths, analcime. Dlegenetic processes and products at NTS have been described by Hoover (1968) and Moncure and others zones contain heulandite and smectite. (1981). Core from drill hole USW GU-3 (sample at Drill cores, sidewall cores, and out- 364.2 m. depth) contains an excellent crop samples from Yucca Mountain, Busted example of such alteration. The textural Butte, and vicinity contain examples of association of heulandite and smectite zeolitized tuff that may not have resulted with devitrificatlon products suggests from diagenesis. The lower vitrophyre that the hydrous minerals may have crys- (densely welded glassy tuff) In the Topo- tallized during subaerial cooling of the pah Spring Member of the Paintbrush Tuff tuff (Levy, 1983). has been altered to smectite and the The degree and extent of alteration zeolite heulandite along the boundary within the vitrophyre are highly variable between the vitrophyre and overlying (Fig. 10). At some sites, the hydrous devitrified densely welded tuff. This minerals form only a thin rind along the boundary, as seen In outcrop at Busted boundary between devitrified tuff and Butte and In drill holes, FIg. 10, Is vitrophyre and Comprise about I wt% or actually a transition zone about 6 m. less of the altered vitrophyre (e.g., thick with interpenetrating lobes of drill core USW GU-3, outcrop at Busted vitric and devitrifled tuff. Fractures Butte). Elsewhere the vitrophyre Is extending downward Into the vitrophyre are highly altered to depths of up to 15 m. bordered by devitrified zones, composed below the devitrifted-vitric boundary and mostly of feldspar and cristobalite (Vani- locally contains up to about 15 wt% heul- man and others, in preparation) as much as andite and 60 wt% smectite, based on x-ray 0.3 m. thick. The outermost portions of diffraction (e.g., sidewall core USW H-5 these fracture-controlled devitrified and drill core UE25a-1). The reasons for 19 ANDER & OTHERS this variability are unclear. Highly controlled by N43-60*E trending altered vitrophyre has been observed only Tertiary left-lateral strike-slip In drill cores (it may weather too easily faults of the Spotted Range-Mine to be preserved In outcrop), which provide Mountain structural zone. minimal Information about possible alter- ation-controlIing factors such as fracture 1.9 Checkpoint Pass. abundance. The proposed exploratory shaft at the USW G-4 site may answer some of 3.3 STOP 8. ORIENTATION STOP. these questions. Turn left off road at Pump Station No. 4. DAY 2 Facing north and looking counter-clock- wise: Ranger Mountains at 2:00 are com- Mileage posed of southeast dipping Paleozolc rocks 0.0 Leave Mercury heading north on Mer- from carbonate rocks of the Ordovician cury Highway (Fig. 1) from housing Pogonip Group through Devonian Nevada area. View of Red Mountaln-Mercury Formation. Older Tertiary gravels form Ridge geology (Barnes and others, low hills In foreground. At 1:00 Is 1982). Red Mountain, between 9:00 Frenchman Lake playa and beyond Is Nye and 12:30, Is composed of gray and Canyon containing several basalt centers brown Ordovician Antelope Valley dated between 6.0 and 7.0 m.y. old (R. F. Limestone through Eureka Quartzite on Marvin, written commun., 1980). High peak left, Ely Springs Dolomite and Silu- on skyline is Bald Mountain in the Groom rian dolomite on right. Strata on Range 80 km. to NNE. French Peak and Red Mountain generally dip eastward. Massachusetts Mountain at 12:00 on the Mercury Ridge, between 1:00 and 2:00, northwest side of Frenchman Flat consist Is composed mainly of Devonian Nevada primarily of faulted Paintbrush and Timber Formation and Devils Gate Limestone. Mountain Tuffs. Flat-topped mountain on North Ridge, between 2:00 and 3:00, distant skyline at 11:30 Is Oak Spring Is composed of Middle and Upper Butte at north end of Yucca Flat. Stratl-. Cambrian carbonates thrust over graphic relationships In the areas of Devonian and Mississippian rocks Yucca and French Flats are shown In Fig. (Spotted Range thrust) In the axial 11. At northwest corner of Frenchman Flat portion of the Spotted Range syn- are CP Pass and CP Hogback (named after cine. South Ridge, between 2:30 and Control Point Headquarters). To left of 4:00 consists of Ordovician through CP Pass are the CP Hills composed of Mississippian rocks that form the MIssissipian and Cambrian rocks overlain southeast limb of the Spotted Range by Tertiary volcanics. High skyline In syncline. Tower Hills, at 4:00, are -far distance at 11:00 is Rainier Mesa. Devils Gate Limestone. Specter Range Directly to the left of Rainier Mesa on In distance, between 7:00 and 9:00, the skyline Is Tippipah Point. At 10:00 contains Cambrian through Devonian on skyline Is Shoshone Mountain which rocks, and a major thrust fault forms part of the southeast rim of Timber (Specter Range thrust) that brings Mountain caldera. In the Intermediate Upper Cambrian and Ordovician rocks foreground at 10:00 are the Intermediate over middle and upper Paleozolc lavas of the Wahmonte-Salyer volcanic rocks, a structural situation similar center on the northeast end of Skull to that mentioned at Stop 1 In the Mountain. Hampel Hill at 9:30 In inter- southwestern part of the Spotted mediate distance Is capped by the Ammonia Range. The Spotted Range thrust and Tanks Member of the Timber Mountain Tuff, the Specter Range thrust may be parts which is underlain by eolian sandstone. of a single major thrust system (CP At 10:00 and 2:00 in the near distance thrust) In the Test Site area. (1.6 to 3 km.) are hills of TertIary Northeast-trending topography is gravels and tuffaceous sedimentary rocks 20 NEVADA TEST SITE GEOLOGY NORTH SOUTH Spring Butte r .rG GROUSE CANYON QTaI ALLUVIUM E,.' MEMBER, BELTED PS ROCKS OF PAVITS SPRING [ ,^ . P 4~~RANGE TUFF F7 lTIMBER MOUNTAIN TUFF E3 TUB SPRING MEMBER, M BT7ELTED RANGE TUFF HORSE SPRING FORMATION TU1FF Y TUFF OF YUCCA FLAT M SHINGLE PASS AND [II]PAINTBRUSH F71~~~~~L~ MONOTONY TUFFS CWAHMONIE- SALYER RED ROCK VALLEY TUFF TUFFS AND TUFFACEOUS L'X\J SEDIMENTS, UNDIFF. I;; COLLUVIUM AND Hul STOCKADE WASH TUFF FRACTION TUFF * CARBONACEOUS CLAYSTONE FM PALEOZOIC ROCKS FIGURE 11: Diagrammatic cross-section from Oak Spring 8utte to northwestern Frenchman Flat, Nevada Test Site, Stops 8 and 10. of Pavits Spring Formation. Light-colored at approximately this point and lacustrine limestones of the underlying continues northeast to foot of Ranger Horse Spring Formation are seen at 7:00 to Mountains. 8:00 where they onlap or are faulted against the Paleozoic rocks. The Horse 7.0 Gravel pits to right provide material Spring contains a tuff bed dated at 29.3 used In the stemming of drill holes m.y. (Marvin and others, 1970), which Is used for nuclear tests. Thickest probably airfoll of the Needles Range alluvium (1220 m.) in Frenchman Flat, Formation of eastern Nevada (Barnes and as determined by gravity, Is approxi- others, 1982). Continue north on Mercury mately 3 km. northwest of Frenchman Highway. Lake. 5.3 At junction of Mercury Highway and 5A 10.0 Y In road. At 9:00 observe struc- Road proceed straight on 5A Road Into tures tested by nuclear blasts. Frenchman Flat. 11.6 At 10:00 dark reentrant Is vitrophyre 6.0 To left, look along Rock Valley where lava of the Wahmonie Formation onlap- Quaternary fault scarps have been ped by Topopah Spring Member of the recognized. Fault zone crosses road Paintbrush Tuff. 21 ANDER & OTHERS 12.5 Turn left. 12.9 STOP 9. RADIONUCLIDE MIGRATION. Turn left onto gravel road. Radionuclide Migration project site (Fig. 12). The RNM project was Initiated In 1974 to study rates of the underground migration of radionuclides from explosion-modifled zones at NTS. The Cambric event, deto- nated In Frenchman Flat In 1965 was chosen for the study for several reasons. The Cambric explosion cavity Is within the NTS Area 5 water-supply aquifer, where leakage could have contaminated the water supply. Hydrologic modeling indicated that suffi- clent time had elapsed for ground water to fill the cavity and chimney to the preshot static water level, which Is 73 m. above the detonation point. The Cambric detona- tion point Is only 294 m. below ground surface, and thus the re-entry drilling and sampling operations were less diffi- cult and expensive than for more deeply 0 7 2 burled tests. The site Is also far enough KM from the areas of active nuclear testing CONTOUR INTERVAL 30.5 M so that damage or interruption of the re-entry and sampling operations from FIGURE 12: West-central Frenchman Flat, those activities Could be unlikely. Suf- showing location of the RNM Experiment No. ficient tritium ( H or T) was present to I site (Stop 9). provide an easily measurable tracer for water from the cavity region. The post- shot debris and ground water in the cavity and chimney also contained enough pluto- artificial gradient to draw water from the nium, uranium, and fission products so Cambric cavity and provide an opportunity that they could be measured and compared. to study radlonuclide transport under The small nuclear yield from the Cambric field conditions. event was expected to have little effect The RNM-25 satellite well has been on the local hydrology. Further, It was pumped at the rate of about 600 gal./- judged that the alluvium constituted a minute. Samples are analyzed weekly for good medium for hydrologic studies because tritium. Beginning in the summer of 1978, it was more permeable than tuff and did tritium was first detected and reached a not have large fissures or cracks through peak of 7000 pCi/ml by late summer of which the water might selectively flow. 1980, when the concentration of tritium The Cambric field studies can be divi- began to decrease. By September 30, 1982, ded Into two phases. (1) The Cambric over 42 percent of the tritium from Cam- cavity region was re-entered In 1974, and bric had been removed by the satellite samples were taken to determine the radio- well. These tests significantly enhance nuclide distribution between the solid our understanding of the ground water material and water. (2) Beginning in transport of radionuclides from nuclear October 1975, water was pumped from a explosion cavities In general (Daniels, satellite well located 91 m. from the 1983). Cambric cavity; this induced a sufficient At 8:00 - 10:00 ENE-trending Quaternary 22 NEVADA TEST SITE GEOLOGY EXPLANATION - CONTACT BETWEEN BEDROCK AND ALLUVIUM - FAULT-DOTTED WHERE BURIED ft' FAULT OR FRACTURE OF QUATERNARY AGE FEB 19 19731j EARTHQUAKE EPICENTER SHOWING THE TWO FAULT-PLANE SOLUTIONS AND PRESSURE AXIS (heavy line), AND DATE AFTERSHOCK EPICENTER SHOWNG PRESSURE AXIS O3tO <,>^ >;^ az 1~~~~~~~~~~~~36-45' FIGURE 13: Southern YUCCa Flat and Frenchman aroea, showing structural pattern, Quaternary faults and fractures, and location of earthquakes, their aftershocks, fault-plane solutions, and pressure axes (Stop 10). fault scarps may be visible In fans at the base of the Ranger Mountains. Return to 20.5 CP Hogback at 1:30 Is composed of paved road, turn left. faulted blocks of Ammonia Tanks Member of Timber Mountain tuff dip- 15.4 Turn right at junction with Mercury ping toward you. Highway. Wahmonie rhyodacitic lavas form hills to west. 22.3 Cambrian Carrara Formation at 11:00 Is folded Into asymmetric anticline 17.0 Intersection of Mercury Highway and (McKeown and others, 1976). Topopah Cane Spring Road. Spring vitrophyre at 10:00; the same unit forms the low hill at 1:00, 18.0 Dark layer low on cliff at 3:00 Is where It Is faulted against the late Wahmonle lava underlying vitro- Ammonia Tanks. phyre of the Topopah Spring Member. 23.7 Crest of CP pass. 18.5 In distance at 10:30 Is blue-gray Cambrian Bonanza King Formation 24.7 STOP 10. NEWS KNOB. Limestone thrust over brown argil- Turn right onto road north of ware- lites of the Mississiplan Eleana house by News Knob. Facility to west Formation, overlapped by Tertiary Is Control Point (CP), which houses volcanics. equipment used to monitor nuclear 23 ANDER & OTHERS Yucca-Frenchman right-lateral shear and fIexure zone (FIg. 13). This structure trends northwest for about 40 km. from the Spotted Range, across northern Frenchman Flat, through the hills between Yucca and Frenchman Flats, and along the southwest- %_b) ern side of Yucca Flat. It is exposed only In.the hills southeast of Yucca Flat, where it consists of a complex shear zone exhibiting right-lateral drag. This zone also marks the termination of a major system of northeast-striking, essentially CONTOUR INTERVAL left-lateral faults. Major fault zones of 200 Mets this Spotted Range-Mine Mountain structu- ral zone Include the Mine Mountain, Cane Spring, and Rock Valley faults. Extensive drill-hole data collected in Yucca Flat have been used to construct Isopach and structure contour maps of Cenozoic units occupying the basin. The configuration of these units indicates that the north- trending faults controlling present-day +j N810.O00 basin morphology were Inactive during E700,000 deposition of volcanics from approximately 25 to 11 m.y. However, after 11 m.y., the overlying sedimentary sequence was strong- FIGURE 14: Isopach map of late Tertiary ly Influenced by these faults. In parti- and Quaternary alluvium In Yucca Flat cular, an Inordinately thick section of (Stop 10). late Tertiary and Quaternary alluvium occurs at the southwestern end of Yucca Flat (Fig. 14). It Is probably a pull- tests. Climb News Knob. apart developed at the intersection of the north- and the northeast-trending faults Facing northward, at 3:00 to 1:00 is (Ander, 1983; Ander and Oldow, 1983; Halfpint Range; at 1:30 Slanted Buttes Is Ander, 1984), or between the north-trend- capped by Rainier Mesa Member; at 1:00 is ing Carpetbag fault and Yucca-Frenchman Banded Mountain (type locality of the shear and flexure zone (W. J. Carr, In Banded Mountain Member of the Bonanza King prep.). Geologic relations, as well as Formation). At 12:00 Is Oak Spring Butte slickenside analyses, Indicate that the cut on the east side by the Butte Fault (a pull-apart, along with much of Yucca Flat, northward extension of the Yucca Fault) was formed during a N78W directed exten- which drops the caprock of Grouse Canyon sion. Sometime after deposition of much Member 425 km. down to the east; to the of the alluvium, probably about 8 m.y. left of Oak SprIng Butte Is ArgiliIte ago, the extension direction rotated to Ridge and Twin Peaks, which Is on the east the currently active direction of N60W flank of a broad depositional syncline In (Ander, 1983; Ander and Oldow, 1983; Tertiary tuffs and underlying sediments Ander, 1984). Schematic east-west cross- with thin laminae of coal. At 10:00 - sections of north, central, and south 11:00 is Rainier Mesa, at 9:30 is Tlppipah Yucca Flat are shown on Fig. 15. Point, to the west at 7:00 to 10:00 are In the last 5 years, during operation Paleozoic rocks of the CP Hills. of the southern Great Basin seismic net, The southwest edge of Yucca Lake playa the Yucca-Frenchman shear and flexure zone Is parallel to and coincident with an has been a boundary between the selsmical- element of the Walker Lane belt -- the ly active Spotted Range-Mine Mountain 24 NEVADA TEST SITE GEOLOGY CARPETBAG EAST ELEVATION ELEV-ATION WEST FAULT YUCCA IN FEET ZONE FAULT IN FEET 000 4000 2000- SEA2000 SEA LEVEL SEA LEVEL TIMBER MTN. TUFF 4000 11 my. 2000 TUFF SEA LIVEL PALEOZOIC CARPETBAG EAST ELEANA ELEVATION FAULT YUCCA ELEVATION FM. IN FEET ZONE FAULT IN FEET - - L000 . . H L. 2000 - - ~~~~~~SEALEVEL FIGURE 15: Geologic sections across Yucca Flat (Stop o0). structural zone to the southwest, and a playa the cracks trend at right angles to much lower rate of activity to the north- the gravity gradient and to the side of east. Before the present seismic network, the basin, contrary to what would be two mediumsized earthquakes (ML 3.5-4.0) expected of they were caused by shrinkage occurred near the Yucca-Frenchman shear resulting from dessication; (4) one of the and flexure zone, one in 1971 at the cracks Is aligned with a small fault scarp intersection of the Cane Spring fault (now obliterated) In alluvium, which In zone, the other In 1973 near the Inter- turn trends toward a bedrock fault just section of the Rock Valley fault zone. In south of News Knob; (5) topographic and the case of the event near Yucca playa leveling data for Yucca playa indicate no (the Massachusetts Mountain earthquake), subsidence has occurred In the area of the slip occurred as either right-lateral cracks, as might be expected with loss of motion on a northwest-striking fault soil moisture; (6) large quantities of plane, or left-lateral motion on a north- water flow into the cracks when they are east-striking fault plane. new, Indicating they go to considerable Yucca and Frenchman playas display a depths, probably Into rocks beneath the feature found In most playas In tectonl- alluvium; (7) although no vertical offset cally active areas: tension cracking. occurred across the cracks, detailed Air photos show that Frenchman Lake playa topography suggests slight displacements cracked at some time Just before 1950, as In alluvium beyond the northeast end of did Yucca playa, but cracking, now nearly the cracks. obliterated, recurred on Yucca playa In Return to Mercury Highway and turn 1960, 1966, and 1969 (Fig. 16), migrating right. In a southeastward direction. The evi- dence that the cracking Is tectonic and 25.2 Orange Road Junction on left, weather not due to dessication Is as follows: (1) station on right. the cracks In Yucca playa and In all the other playas of the region trend consist- 27.0 Tweezer Road on right. Mine Mountain ently north to northeast, regardless of at 9:00 has Devonian carbonate rocks playa shape; (2) the cracks tend to be thrust over Mississiplan Eleana curvilinear, not polygonal; (3) In Yucca Formation (Orkild, 1968; Stop 16). 25 ANDER & OTHERS consists of a series of east-dipping Basin and Range style faults which traverse the length of Yucca Flat on the western side (D. L. Healey, unpublished gravity data). Average post-tuff dip-slip displacement Is 600 m.; right-lateral motion of as much as 600 m. has also been postulated (Carr, 1974). Two major fault scarps of the sys- tem were propagated to the surface as a result of the detonation of the Carpetbag event In 1970. This event also caused the Carpetbag sink and a series of concentric cracks extending out about 1000 m. from the edge of the sink. This type of sur- face cracking may have been due to detona- tion of the nuclear device below the sta- tic water level, a practice now avoided. The graben bounded by the two fault scarps extends for about 2600 m. on the western side, where 11 to 590 cm. of post-testing dip-slip displacement has FIGURE 16: Map of Yucca Lake playa area been documented on the western fault showing cracks (lettered A to F) and scarp. On the eastern side, three fault detailed topography. Shaded area Is strands ranging In trend from N-S to N40-E apparently depressed with respect to (E. C. Jenkins, written commun., 1973) unshaded areas, based on distribution of form two major scarps, 1525 m. long, with water In the lake In March 1973 (Stop 10). dip-slip displacements of 9 to 490 cm. About 0.9 m. of right-lateral motion has been recorded along the system since 1970. Ramp features extending northeast from 28.0 Area 6 Blrdwell casing yard. the northern end of the western fault scarps have surfaces which dip 10- to the 31.5 Brick houses at 9:00 are structures southeast and are bounded by low scarps at built during era of above-ground the toe of the slope. Trenching reveals nuclear testing. that the ramps are shallow features which die out a short distance from the main 31.8 Reynolds Electric Company drilling fault. The ramps are proposed as result- support yard. Ing from one or more of the following possible causes: (1) surface expression 33.1 At Y In road veer left onto Rainier of splays or "horsetails" from the main Mesa Road. Carpetbag fault; (2) lowering of ground- water table causing surface subsidence; 45.5 East-facing Yucca Fault scarp at and (3) underground nuclear testing caus- 3:00. ing differential ground subsidence. Surficial deposits exposed In the wall 46.4 Turn left onto Road 2-04- (marked of the graben help constrain the ages of U2FA). recent fault movement. Young fluvial sands, gravel, and slope-wash post-date 47.2 STOP 11. MORPHOLOGY OF THE CARPETBAG the last major movement on the Carpetbag FAULT. fault. These deposits have stage I sotl- Park bus and walk 0.3 miles to Car- carbonate morphology of Glle and others petbag Fault scarps (Fig. 17). (1966) and are probable equivalents to Holocene units described by Hoover and The north-trending Carpetbag fault system others (1981). The older units pre-dating 26 - w NEVADA TEST SITE GEOLOGY fault movement have a thin K horizon with stages III to IV morphology and have uranium-trend dates of 270,000 to 310,000 yrsa. (J. N. Rosholt, written commun., 1983). Uranium-series dating of secondary carbonate along fractures brackets the displacement between 93,000 and 37,000 yrs. (Knauss, 1981), which correlates well with the lack of distinguishable fault scarps In the younger (Holocene?) gravels prior to nuclear testing In 1970. 48.0 Turn left on Rainier Mesa Road then turn right on 2-05 Road (Fig. 17). 49.6 Yucca fault scarp (early Holocene) In foreground at approximately 12:00 Is 18 to 24 m. high. Climax stock In background. 51.0 Yucca fault scarp crosses road. Roughness of road Is due to repeated fault displacement triggered by nearby nuclear tests. FIGURE 17: Carpetbag fault system (Stop 51.7 Turn right to Sedan Crater. 11). 52.1 STOP 12. CONTAINMENT GEOLOGY. Underground tests require a comprehensive tests are conducted In alluvium or tuff geologic site characterization to help but some have been In carbonate or grani- ensure complete containment of radioactive tic rocks. Once the geologic setting is debris and gases created by the nuclear understood, the response of the medium to explosion. Based on device parameters an the explosion Is predicted and the poten- appropriate site Is selected. Following tial for complete containment of the completion of the emplacement hole, using radioactivity Is evaluated. Not until the large-hole (up to 3.7 m. In diameter) site has been thoroughly reviewed and drilling techniques developed at the NTS, approved by the Department of Energy's It Is sampled and logged with large dia- panel of experts Is the experiment allowed meter tools that are also unique to the to proceed. test site. These data are evaluated and The explosive device Is placed Into a the detailed site characterization is pre- large rack which contains the diagnostic pared (Fig. 18). Items of Interest are systems. This rack Is lowered Into the the mineralogy/petrology, stratigraphy and hole, along with more than one hundred structure, surface features both natural power and signal cables, using a wire rope and cultural, densities, moisture con- harness on a large crane. After tents, non-condensible gas generation detonation, the effects on the geologic (CO2 ), depth to the static water level, medium are evaluated through surface acoustic Impedances and any features which- mapping, ground motion measurements, are unusual. Adequate characterization seismic Information and other data as often requires the drilling of exploratory available. holes, detailed geophysical surveys, and Peaceful nuclear explosions in the other specialized Investigative techniques U.S., as encompassed In the Plowshare such as borehole photography. Most of the Program, began as a series of meetings and 27 ANDER & OTHERS 54.1 Turn right on Road 2-07. 56.6 Turn right onto Rainier Mesa Road. 60.8 Area 12 camp on right. At 3:00 are the orange to brownish-gray tuffs of the Miocene Tunnel Beds. The welded unit overlying the Tunnel Beds ap- proximately 2/3 of the way to the top Is Miocene Grouse Canyon Member of the peralkaline Belted Range Tuff. Keep to left on Stockade Wash high- 0 Osa 1COD way, continuing southward toward pass at south side of Rainier Mesa. FIGURE 18: Geologic sectIon through an emplacement site (Stop 12). 62.5 Thrust fault between the Devonian Devils Gate limestone and Missipplan panels In 1956. Massive nonnuclear high- Eleana on right. explosive excavation and fracturing ex- perlments were conducted at the Nevada 63.1 To left observe Tunnel Beds filling Test Site to derive proper scaling ldws to paleovalley In Eleana Formation. be applied to the use of low to Inter- Bright red zones are areas of Intense mediate yield nuclear explosives for weathering and alteration. excavations. In all, some 15 nuclear cratering experiments were conducted 64.3 Tuff/Paleozolc contact, very altered. between 1962 and 1968, with a few experi- mental underground applications, mostly 65.6 STOP 13. ORIENTATION. gas stimulation, taking place In New Pass on south side, Rainier Mesa (see Mexico and Colorado (Projects GNOME, Fig. 1). Walk approximately 100 m. GASBUGGY, RULISON, RIO BLANCO) as late as to eastern overlook. May 1973. The USSR has used nuclear explosives for oil and gas stimulation as To the east Is erosional unconformity of well as for construction of earthen dams. Tunnel Beds on Eleana. In distance to SEDAN crater, created In one second on northeast Is the Groom Lake Playa. Pahra- July 6, 1962, testifies to the excavation nagat Range on skyline. On Survey Butte, ability of nuclear explosives. A 100 kT just to left of Area 12 camp are small device was detonated at 193.5 m. depth In faults in Rainier Mesa Member. In same tuffaceous alluvium. The resultant Crater area welded Grouse Canyon Member can be Is 390 m. In diameter, 97.5 m. deep, aqd seen filling erosional valleys In Tunnel has a volume of approximately 5 x 10 m Beds. The heIght of the lip ranges from 6 to 30 m. above preshot levels. Ejecta were LUNCH. Return to Stockade Wash Highway, found as far as 1770 m. from ground zery6 turn right. The seismic energy release was 2.45 x 10 ergs, equivalent to an earthquake magni- 66.8 Stockade Wash Tuff forms bluffs on tude of 4.8. A cross-section through the either side of Stockade Wash and crater lip (Fig. 19) shows thrusted and thickens westward. Mesas on both overturned marker beds resulting from the sides of road are capped by resis- explosion In this poorly indurated allu- tant ledges of Tiva Canyon and vium. Rainier Mesa Members, down-faulted to the west along outer ring frac- 52.5 Return to paved road and turn left at ture faults associated with the stop sign. Timber Mountain caldera collapse. 28 U NEVADA TEST SITE GEOLOGY 67.3 Wide valley held up by dip slope of westward toward Split Ridge. densely welded (erosion resistant) but unexposed Grouse Canyon Member. 77.2 STOP i4. PAHUTE MESA (see Fig. 1). Configuration of less resistant on Bus drops participants off and resistant units allows valley to continues to Echo Mesa Road to turn widen but Inhibits downcutting. around (1.1 km.). 69.3 Intersection with Pahute Mesa Road, To south overlooking Big Burn Valley, continue straight ahead. cuestas of Ammonia Tanks 4 km. away are dipping Into the Timber Mountain caldera, 69.6 Road parallels rim of caldera marked with Stockade Wash Tuff and Grouse Canyon by cuesta of onlapptng intraceldera Member forming the walls of the caldera. Ammonia Tanks Member to left. Flat- On the distant skyline to the south, lying tuffs of Area 20 underlying rhyolite of Shoshone Mountain overlies the Stockade Wash Tuff to the right. southeastern caldera wall and rim. Visl- ble on the far skyline to the southeast 70.8 At 1:00 Is Rattlesnake Butte capped are the Spring Mountains. Rainier Mesa by Rainier Mesa Member. Road goes can be seen to the left capped by Rainier up dip slope of welded peralkallne Mesa Member; the bench partway up side of Grouse Canyon. mesa Is formed by Tiva Canyon Member. Cuestas ringing Big Burn Valley are welded 71.8 Road cut exposes peralkaline airfall Grouse Canyon Member. tuff above welded Grouse Canyon. At In the road cut we see bedded vitric 12:00, upthrown fault block approxi- tuff of Area 20. At the western end of mately 1 km. from road Is welded the road cut, this tuff Is overlain uncon- Grouse Canyon. formably by a 2-3 cm. thick ash fall and the base surge of the Rainier Mesa Member. 73.1 Contact between Grouse Canyon welded The entire section of Paintbrush Tuff Is tuff and underlying Grouse Canyon absent here. Although the spectacular airfall tuff. erosional unconformity might suggest erosional stripping of the Paintbrush, no 74.8 Grouse Canyon airfall tuff thickens Paintbrush equivalent other than the GRAVEL MARKER BED "A" !0 700 Modified from Short (?964J DISTANCES FROM GZ FIGURE 19: Geologic section through the Sedan Crater lip exposed In cross section trending N38'W from ground zero (Stop 12). 29 ANDER & OTHERS uppermost member, the Tiva Canyon has been lavas of Buckboard Mesa. The basalts found by geochemical sampling In this were erupted where Basin and Range general area. The absence of Paintbrush faults Intersect Inner caldera ring Tuff at this exposure and the thinning of fracture zone. the Rainier Mesa Member towards the south- ern rim of Pahute mesa Indicates that the 91.2 Cuesta of Ammonia Tanks Member, which rim of Pahute Mesa was topographically was banked into scallop of caldera. high during all of Paintbrush time. To the northwest of us Is located a 91.5 Unconformable contact and debris major volcano-tectonic subsidence feature, flows between Split Ridge lavas to 47 the Silent Canyon caldera of Orkild and left and Ammonia Tanks tuff to right. others (1968). This Is actually a very complex feature, all but hidden beneath 92.2 At 9:00 Is Split Ridge lava overlain outflow sheets from the Timber Mountain by bedded peralkaline tuffs and caldera to the south. The earliest vol- welded Grouse Canyon Member. canism associated with she Silent Canyon center erupted >200 km of comenditic 92.6 STOP 15. TIMBER MOUNTAIN CALDERA (highly alkallc rhyolite) magma, largely (Fig. 20). beneath Pahute Mesa and the Belted Range to the east (Noble and others, 1968). Here we are In a deep paleotopographic Major outflow sheets are the Tub Spring "scallop" in the wall of Timber Mountain and Grouse Canyon Members of the Belted caldera (Byers and others, 1976a). At Range Tuff, the latter (younger) unit this scallop the topographic wall of the exposed In the valley below. Calcalkallne caldera changes direction from northerly volcanics containing Mg-rich mafic mine- to westerly. This wall Is the result of rals are Interbedded with the Belted Range cauldron subsidence rel 3 ted to the erup- Tuff. tion of more than 1250 km of the Rainier Following cessation of comenditic Mesa Member, the older of two major ash- volcanism, a sequence of calcalkaline flow tuff sheets of the Timber Mountain volcanics containing Fe-rich mafic mine- Tuff (Byers and others, 1976b). The rals was erupted. These are the tuffs and caldera collapse associated with the lavas of Area 20 at Pahute Mesa, and the younger ash-flow sheet, the Ammonia Tanks Crater Flat Tuff, tuffs and lavas of Member, Is nested within the collapse area Calico Hills, and the rhyolitic (lower) associated with the eruption of the Rain- portion of the Topopah Spring Member of ler Mesa (Byers and others, 1976a, 1976b). the Paintbrush Tuff at Yucca Mountain. Timber Mountain resurgent dome in the cen- Return to bus and continue down Pahute tral part of the caldera (Carr, 1964; Carr Mesa Road. and Quinlivan, 1968) occurred soon after collapse related to the Ammonia Tanks 85.2 Turn right (south) on Pahute Mesa Member and exposes about 1000 m. of the Road. Intracaldera facles of the Ammonia Tanks (Byers and others, 1976a, 1976b). 85.9 Turn right on airstrip road entering At Well 8 (Fig. 20), the cuesta rim to caldera. Ammonia Tanks Member at the south is an eroded rim of onlapping 3:00. Ammonia Tanks ash-flow tuff, underlain by Interbedded coarse reworked tuff and 86.4-87.4 Traverse alluvial caldera fill. cauldron subsidence-related debris flows. To the north, the rim of the caldera wall 89.4 End of pavement. Is welded Grouse Canyon underlain by bedded peralkalIne tuff onlapped by the 89.5 Turn right onto Road 18.01. At 7:00 upper lithic-bearing, Intracaldera Rainier to 8:00 Is Timber Mountain resurgent Mesa Member of quartz latitic composition. dome. Also to southwest are 2.8 Lithic clasts In the Rainier Mesa are m.y.-old basalt cinder cones and derived not only from the welded Grouse 30 NEVADA TEST SITE GEOLOGY Canyon rim above but also from a basal NOMW SOW partially-welded rhyolitic Rainier Mesa ash-flow, which was formerly In the cal- dera wall above the Grouse Canyon but is now eroded away. Sparse granitic xeno- liths, presumably from depth, Indicate crystalline rocks above the magma chamber at the site of Rainier Mesa ash-flow tuff vent(s). Well 8 penetrated 45 m. of quartz latitic facles of the uppermost Rainier Mesa Member before penetrating precaldera rocks. The quartz latite .i. cm mwi'-Tt-Tud *mfl Tpb- Bedded Tuft represents the lowest erupted portion of e2 T -Amons Tank MwnhW I Tvw. Stockde Was Tuff U*Tar - Rlain..Mur Martemri Tbg -G musCaYny UMor ws the magma column, 11.3 m.y. ago (Marvin Tv -R ...wed tuft '(aVedded - tuft and others, 1970). TdO- Dobri fw I o FIGURE 20: Sketch of geologic relations 95.6 Turn left onto Airstrip Road. at Well 8 (Stop 15). 99.3 Turn right on Pahute Mesa Road. several drill holes were drilled on 99.6 Road parallels wall of caldere, with the flanks of SynclIne Ridge to test Intracaldera Ammonia Tanks on right the underlying argillite of the lapping on wall of Stockade Wash Eleana for suitability as a nuclear Tuff underlain by Grouse Canyon waste repository. The site was Member. rejected, primarily because of Its proximity to nuclear testing. 101.7 Leave caldera wall. At 12:00 are Big Butte and Sugar Loaves capped by 110.9 Turn right on Orange Road (TTppipah Tiva Canyon Member. At 9:00, Pinyon Highway). Butte. 116.2 Turn right on Mine Mountain Road. 103.5 Altered multi-colored tuffs and thin Grouse Canyon Member cut by minor 118.1 Entering east side of Mine Mountain, fault crossing the road. Devils Gate Limestone thrust over Eleana Formation. 104.1 Contact between Red Rock Valley Tuff and underlying Eleana Formation at 118.4 Thrust contact between red Eleana 1:00. Valley at 9:00 to 12:00 Is argillite and upper plate of light type locality of Red Rock Valley gray Devils Gate Limestone. Tuff. 118.7 Structure to left Is old mercury 104.4 On left, contact between Red Rock retort. Valley Tuff and Eleana Formation In road cut. 119.5 STOP 16. MINE MOUNTAIN THRUST. 106.7 Highway parallels Syncline Ridge at The route to this stop crosses the Mine 12:30 formed by Pennsylvanian Tippl- Mountain thrust fault, which separates pah Limestone. argIllite of the Mississippian Eleana Formation In the lower plate from carbo- 109.0 Pass the axial trace of Syncline nate rocks of the Devonian Devils Gate RIdge, best exposed on right (south) Limestone and Nevada Formation In the side of bus, 1100 m. of Pennsylva- upper plate (Fig. 21). Overlook Point nian Tlppipah Limestone Is exposed offers an excellent panorama of Mine In the west limb. From 1977-79, Mountain thrust and of Yucca Flat. 31 ANDER & OTHERS Allvium and Volcanic Quatemary-Teniary ELEAA4 FORMTION Unit I Mississipian 37" . Unit H I NEVADA FORMATION UpPoer and Lower Parts Devils Gate Limestone Devonian IZ I and Nevada Formation, v/2zzzz] Undivided Dolomite of Sootted cog~ange, Undivided Silurian Em Antelope Valley Ordovician Thrust Uinestone 4'w "? Thrust Fault, Sawteeth on Upper Plate Gravity Slide Fault, Sawteeth on Upper Plate Normal Fault. Bail on Downthrow Side 0 1mile SOLE OF V7'3' N A GRAVITY SLIDE SHEET I A i- I 0 I km I _IqLw FIGURE 21: Geology In vicinity of Mine Mountain (Stop 16.) Several thrust faults In the region of derance of evidence suggests that folding the NTS emplace upper Precambrian and and thrusting occurred at moderate depths lower Paleozoic rocks on top of middle and during Mesozoic time. Most of the thrust upper Paleozolc rocks. These occurrences plates have been extensively sliced by Include the Mine Mountain and CP thrusts strike-slip faults and by later normal In the Yucca Flat area, the Specter Range faults during Tertiary time. Bus con- thrust west of Mercury, and the Spotted tinues on to Mid Valley and turns around Range thrust (also seen from Stop 1) east for return (6 km.). of Mercury. Similar klippen are distrlbu- ted over a distance of 120 km. along 122.8 Turn right on Tippipah Highway for north-trending axes of major synclines return to Mercury. east of the Test Site. Regionally the direction of movement Is toward the south- 150.6 Exit NTS at main guard station In east but local underthrusting, as In the Mercury. Turn In badges, RAD-safe CP hills, has resulted in some overturning check. Return to Las Vegas. Hope of folds toward the west. The prepon- you enjoyed the field trip. 32 NEVADA TEST SITE GEOLOGY REFERENCES 919, 70 p. . Carr, W. J., Orkild, Paul P., Ander, H. D., 1983, Ash-flow tuff distri- Scott, R. B., and Warren, R. G., 1983, bution and fault patterns as Indicators Volcano-tectonic relations and some of late-Tertiary regional extension, petrologic features of the Crater Flat Nevada Test Site: Proceedings Second Tuff, southwestern Nevada (abs.): Symposium on Containment of Underground Geol. Soc. Amer. Abstracts with Pro- Nuclear Explosions, Kirtland AFB, grams, v. 15, n. 5, p. 280. Albuquerque, NM, August 2-4, 1983, Carr, W. J., 1964, Structure of part of Lawrence Livermore National Laboratory the Timber Mountain dome and caldera, CONF-830882, v. 1, Clifford Olsen, Nye County, Nevada; in Geological Compiler, p. 155-174. Survey research 1964: U.S. Geol. 1984, Rotation of late Cenozoic Survey Prof. Paper 501-B, p. 816-B19. extensional stresses, Yucca Flat re- aand QuInIlvan, W. D., 1968, Struc- glon, Nevada Test Site, Nevada, Ph.D. ture of Timber Mountain resurgent dome, thesis: Houston, Rice University, 77 Nevada Test Site: Geol. Soc. Amer., P. Mem. 110, p. 99-108. and Oldow, J. S., 1983, Late Ceno- 1974, Summary of tectonic and struc- zolc rotation of extensional stresses, tural evidence for stress orientation Yucca Flat region, Nevada Test Site, at the Nevada Test Site: U.S. Geol. Nevada (abs.): EOS Trans. Amer. Geo- Survey Open-File Report 74-176, 53 p. phys. Union, v. 64, no. 45 (Fall Meet- 1982, Volcano-tectonic history of ing Abstracts), p. 858. Crater Flat, southwestern Nevada, as Barnes, Harley, Ekren, E. B., Rogers, C. suggested by new evidence from drill L., and Hedlund, D. L. 1982, Geologic hole USW-VH-1 and vicinity: U.S. Geol. and tectonic map of the Mercury Quad- Survey Open-file Report 82-457, 23 p. rangle, Nye and Clark Counties, Nevada: , Byers, F. M., Jr., and Orkild, P. U.S. Geol. Survey Misc. Inv. Map I- P., 1984, Stratigraphic and volcano- 1197, scale 1:24,000. tectonic relations of Crater Flat Tuff Broxton, D. E., Vaniman, D., Caporusclo, and some older volcanic units, Nye F., Arney, B., and Heaken, G., 1983, County, Nevada: U.S. Geol. Survey Detailed petrographic descriptions and Prof. Paper 1323 (in press). microprobe data for drill holes USW-G2 Crowe, B. M., and Carr, W. J., 1980, and Ue2Mb-1H, Yucca Mountain, Nevada: Preliminary assessment of the risk of Los Alamos National Laboratory report volcanism at a proposed nuclear waste LA-9324-MS, 168 p. repository In the southern Great Basin, Burchfiel, B. C., 1964, Precambrian and Nevada and California: U.S. Geol. Paleozoic stratigraphy of Specter 52 Survey Open-File Report 80-357, 15 p. Range quadrangle, Nye County, Nevada: , Johnson, M. E., and Beckman, R. J., Am. Assoc. Petroleum Geologists Bull., 1982, Calculation of the probability of v. 48, p. 40-56. volcanic-disruptlon of a high-level Byers, F. M. Jr., Carr, W. J., Christian- radioactive waste repository within sen, R. L., Lipman, P. W., Orkild, southern Nevada, USA: Radioactive Paul, and Quinlivan, W. D., 1976a, Waste Management and the Nuclear Fuel Geologic map of Timber Mountain cal- Cycle, v. 3(2), p. 167-190. dera, Nye County, Nevada: U.S. Geol. , Vaniman, D. T., and Carr, W. J., Survey Misc. Geol. Inv. Map 1-891, 1983, Status of volcanic hazard studies scale 1:48,000. for the Nevada Nuclear Waste Storage Carr, W. J., Orkild, Paul P., Investigations: Los Alamos National Quinlivan, W. D., and Sargent, K. A., Laboratory report LA-9325-MS, 47 p. 1976b, Volcanic suites and related . Self, S., Vaniman, D., Amos, R., cauldrons of Timber Mountain-Oasis and Perry, F., 1983, Aspects of poten- Valley Caldera complex, southern Ne- tial magmatic disruption of a high- vada: U.S. Geol. Surv. Prof. Paper level radioactive waste repository In 33 ANDER & OTHERS southern Nevada: Jour. Geol., v. 91, McKeown, F. A., Healey, D. L., and Miller, p. 259-276. C. H., 1976, Geologic map of the Yucca Daniels, W. R. (ed.), 1983, Laboratory and Lake quadrangle, Nye County, Nevada: field studies related to the radlonu- U.S. Geol. Survey Geol. Quad. Map cide migration project: Los Alamos GQ-327, scale 1:24,000. National Laboratory Rept. LA-9691-PR, Moncure, G. K., Surdam, R. C., and Mc- 63 p. Kague, H. L., 1981, Zeolite diagenesis Fleck, R. V., 1970, Age and possible below Pahute Mesa, Nevada Test Site: origin of the Las Vegas Valley shear Clays and Clay Minerals, v. 29, p. zone, Clark and Nye Counties, Nevada: 385-396. Geol. Soc. Amer. Abs. with Programs Noble, D. C., Sargent, K. A., Mehnert, H. (Rocky Mtn. Sec.), v. 2, no. 5, p. 333. H., Ekren, E. B., and Byers, F. M., Gile, L. H., Peterson, F. F., and Gross- Jr., 1968, Silent Canyon volcanic man, R. B., 1966, Morphological and center, Nye County, Nevada: Geol. Soc. genetic sequences of carbonate accumu- America Memoir 110, p. 65-76. lation in desert soils: Soil Science, Orkild, Paul, 1982, Geology of the Nevada v. 101, p. 347-360. Test Site, In Proceedings First Sympo- Hildreth, W., 1981, Gradlents In silicic slum on Containment of Underground magma chambers: Implications for Nuclear Explosions, Monterey, CA, lithospherIc magmatism: Jour. Geophys. August 26-28, Los Alamos National Res., v. 86(B11), p. 10153-10192. Laboratory Report LA-9211-C, B. C. Hoover, D. L., 1968, Genesis of zeolites, Hudson, E. M. Jones, C. E. Keller, and Nevada Test Site: Geol. Soc. Amer. C. W. Smith, compilers, p. 323-338. Mem. 110, p. 275-284. 1968, Geologic map of the Mine , Swadley, W. C., and Gordon, A. J., Mountain Quadrangle, Nye County, Neva- 1981, Correlation characteristics of da: U.S. Geol. Survey Geol. Quad. Map surficial deposits with a description GQ-746, scale 1:24,000. of surficial stratigraphy In the Nevada ___,_ Byers, F. M. Jr., Hoover, D. L., Test Site region: U.S. Geological and Sargent, K. A., 1968, Subsurface Survey Open-Flle Report 81-512, 27 p. geology of Silent Canyon Caldera, Knauss, K. G., 1981, Dating faults and Nevada Test Site, Nevada: Geol. Soc. associated Quaternary material from the America Memoir 110, p. 77-86. Nevada Test Site using uranium-series ____,_ Sargent, K. A., and Snyder, R. P., methods: Livermore, California, Law- 1969, Geologic map of Pahute Mesa, rence Livermore Laboratory, UCRL-53231, Nevada Test Site and vicinity, Nye 51 p. County, Nevada: U. S. Geol. Survey Map Levy, S. S., 1983, Studies of altered 1-567, scale 1:48,000. vitrophyre for the prediction of nucle- Sargent, K. A., McKay, E. J., and Burch- ar waste repository-induced thermal fiei, B. C., 1970, Geologic map of the alteration at Yucca Mountain, Nevada: Striped Hills quadrangle, Nye County, (abs) Materials Research Society 1983 Nevada: U.S. Geol. Survey Geol. Quad. Annual Meeting Final Program and Ab- Map GQ-882, scale 1:24,000. stracts, p. 222. , and J. H. Stewart, 1971, Geologic Longwell, C. R., 1974, Measure and date of map of the Specter Range NW Quadrangle, movement on Las Vegas Valley shear Nye County, Nevada: U.S. Geol. Survey zone, Clark County, Nevada: Geol. Soc. Geol. Quad. Map GQ-884. Amer. Bull., v. 85, p. 985-990. Short, N. C., 1964, nuclear explosions, Marvin, R. F., Byers, F. M., Jr., Mehnert, craters, astroblemes, and cryptoexplo- H. H., Orkild, Paul P., and Stern, T. sion structures: University of Cali- W., 1970, Radlometric ages and strati- fornia Report UCRL-7787, 75 p. graphic sequence of volcanic and plu- Stewart, J. H., 1967, Possible large tonic rocks, southern Nye and western right-lateral displacement along fault Lincoln Counties, Nevada: Geol. Soc. and shear zones In the Death Valley-Las Amer. Bull., v. 81, p. 2657-2676. Vegas area, California and Nevada: 34 F - NEVADA TEST SITE GEOLOGY Geol. Soc. America Bull., v. 78, p. LA-9707-MS. 131-142. Warren, R. G., 1983a, Geochemical simil- Vaniman, D. T. and Crowe, S. M., 1981, aritles between volcanic units at Yucca Geology and petrology of the basalts of Mountain and Pahute Mesa: Evidence Crater Flat: Applications to volcanic for a common magmatic origin for vol- risk assessment for the Nevada Nuclear canic sequences that flank the Timber Waste Storage Investigations: Los Mountain Caldera, In Proceedings Second Alamos National Laboratory report Symposium on ContaInment of Underground LA-8845-MS. Nuclear Explosions, Kirtland AFS, , Crowe, B. M., and Gladney, E. S., Albuquerque, NM, August 2-4, 1983, 1982, Petrology and geochemistry of Lawrence Livermore National Laboratory hawalite lavas from Crater Flat, Neva- CONF-830882, v. 1, Clifford Olsen, da: Contrib. Mineral. Petrol., v. 80, compiler, 213-244. p. 341-357. 1983b, Geochemical similaritles , 81sh, D., Broxton, D., Byers, F., between volcanic units at Yucca Moun- Helken, G., Carlos, B., Semarge, E., tain and Pahute Mesa: Evidence for a Caporusclo, F., and Gooley, R., In common magmatic origin for volcanic press., Variations In authigenic miner- sequences that flank the Timber Moun- alogy and sorptive zeolIte abundance at tain Caldera: EOS Trans. Am. Geophys. Yucca Mountain, Nevada, based on stud- Union, v. 64, no. 45 (Fall Meeting les of drill cores USW GU-3 and G-3: Abstracts), p. 896. Los Alamos National Laboratory report Publication authorized by the Director, United States Geological Survey. 35 - HYDROGEOLOGY OF THE NEVADA TEST SITE AND SOUTHERN AMARGOSA DESERT (FIELD TRIP 21) Leaders: JOHN W. HESS and ROGER L. JACOBSON, Desert Research Institute, Reno Contributors: CLINTON C. CASE, PAUL R. FENSKE, RICHARD H. FRENCH, JOHN W. HESS, ROGER L. JACOBSON, MARTIN D. MIFFLIN, and STEPHEN W. WHEATCRAFT, Desert Research Institute, Reno INTRODUCTION This trip was formulated to present a broad overview of the hydrogeology of the Nevada Test Site (NTS) and the Southern Amargosa Desert which Is thought to be the discharge area for the regional ground- water flow system encompassing part of the NTS. There has been much Interest In the hydrogeology of the area because of the potential of radionucilde migration away from the site, due to underground nuclear testing and the potential Yucca Mountain High Level Nuclear Waste Repository which might be sited on the western edge of the NTS. The first day field trip begins with a tour of the NTS starting In Las Vegas and ending In Beatty, Nevada where we will spend the night. The next day will be a trip to the Southern Amargosa Desert FIGURE 1 MAP OF FIELD TRIP AREA ending In Las Vegas. Fig. I Is a simpli- fied map of the field trip. combination of the Tonopah Test Range, the Neilis Air Force Range, and the Nevada LOCATION Test Site Is one of the largest unpopula- ted land areas In the United States, The Nevada Test Site Is located In Nye comprising some 15,815 sq. km. County In southern Nevada, with Its south- Fig. 2 shows the general layout of the ernmost point about 100 km. northwest of Nevada Test Site and Identifies some of Las Vegas. The site contains 3,500 sq. the areas within the site. The shaded km. of federally-owned land with restric- areas Indicate principal areas used for ted access. underground testing. The Nevada Test Site Is bordered on Mercury Is the main base camp at NTS. three sides by 10,700 sq. km. of land The camp provides general support facili- comprising the Neillis Air Force Range, ties and overnight accommodations for 960 another federally-owned, restricted area persons. (see Fig. 1). This buffer zone varies from 24-104 km. between the test area and HISTORICAL BACKGROUND OF NTS land that Is open to the public. A north- western portion of the Nelils Air Force Use of the NTS areas prior to 1951 mainly Range Is occupied by the Tonopah Test comprised mining, grazing, and hunting. Range, an area of 1,615 sq. km. The Two Inactive mining districts, Oak Springs 224 NTS & AMARGOSA HYDROGEOLOGY O 10OMILES o 5 10 2OKILOMETERS .> 115 r Crystal Mine I t)? )"Climax Mn 4---= T; * SPRING - RAIN GAGE :.* NUCLEAR TEST AREA . FIGURE 2 NEVADA TEST SITE 225 HESS X JACOBSON and Wahmonle, lie wholly or partially which would be economically recoverable within the borders of the NTS. Oak Spring considering today's mineral requirements. District occupied part of the northeast Other than the deposits In the mining corner of the test site and Included at *districts mentioned above, no additional least two onsite properties, the Climax qualIfying mineral deposits have been Mine and the Crystal Mine, when the NTS found. was established (Area 15, Fig. 2). Pros- Prior to 1955 the NTS area was used for pecting and exploratIon started before cattle grazing, and waterholes were deve- 1905, and numerous smell pits, shafts, and loped and cabins and corrals built at tunnels at higher elevations remain as several points on the site. Impact of the evidence of sporadic activity which con- grazing Industry on the environment, prior tinued until NTS was established. Most of to the establishment of the NTS, was the prospects are at locations showing evidently small and Is now Indiscernible. slight mineralization and low values In In the years Immediately following copper, lead, silver, gold, or mercury. World War 11, nuclear weapons tests were In 1937, low-grade tungsten ore was conducted In the atmosphere or underwater. found In the Oak Spring mining district Before 1951, all of this work was done at near the northeast corner of NTS. This remote Pacific Island sites. When weapons small deposit was outlined as Climax and development was accelerated In 1949 and Crystal ore bodies (Fig. 2) by drilling 1950 In response to the national defense and exploration conducted In 1940. Signi- policy It became Increasingly clear that ficant production of ore did not occur If nuclear weapons could be tested safely until 1956 when high tungsten prices within the continental boundaries, weapons permitted economic extraction of most of development lead times would be reduced the ore. After 10 yrs. of co-use the and considerably less expense Incurred. mining claims were acquired by the govern- At that time, a number of sites throughout ment through routine condemnation proce- the continental United States, Including dures and the owners reimbursed. The Alaska, were considered on the basis of workings have since remained In disuse. low population density, safety, favorable The Wahmonle District, located in south year-round weather conditions, security, central NTS, was prospected about 1905 for available labor sources, reasonable acces- gold and silver ores. No production sibility Including transportation routes, occurred until 1928 when a high grade end favorable geology. Of all the fac- silver-gold ore was rediscovered at the tors, public safety was considered the Horn Silver mine located In Area 26 (Fig. most Important. It was determined that 2). This resulted In minor shipments of under careful controls, an area within ore and caused an Influx of 1,500 people what Is now the Nellis Air Force Range Into Wahmonle. However, after several could be used for relatively low yield shafts and extensive prospecting In the nuclear detonations with full assurance of area revealed no additional ore finds, public safety. Interest rapidly waned and the town was Originally, 1,760 sq. km. were with- abandoned by the summer of 1929. drawn on February 19, 1952, for nuclear In addition to these developments, testing purposes. This resulted In the there Is evidence of sporadic prospecting formation of approximately the eastern throughout the Nevada Test Site. Disrup- half of the present Nevada Test Site. The tion of the landscape by mining and pros- predominant features of this area are the pecting was locally severe, but the total closed drainage basins of Frenchman Flat Impact of these activities on the environ- and Yucca Flat where the early atmospheric ment has been slight. Extensive geologic tests were conducted. The main Control Investigations made by the U.S. Geological Point was located and remains on the crest Survey using samples taken from explora- of Yucca Pass between these two basins tory drill holes, emplacement holes, and (Fig. 2). Additional land withdrawals In tunnels In the areas used for nuclear 1958, 1961, and 1964 added to the site, testing have revealed no mineral deposits and with the use of the Pahute Mesa area 226 NTS & AMARGOSA HYDROGEOLOGY acquired In 1967, provide Its present size January 1983, there have been around 750 of about 3,500 sq. km. announced nuclear tests conducted at the Although the NTS was originaly selected Nevada Test Site. All atmospheric tests to meet criteria for atmospheric tests, It and Plowshare program tests conducted at also has proved satisfactory for under- the Nevada Test Site have been announced. ground tests. For tests of up to one Underground nuclear tests that may cause megaton and for those of a somewhat higher significant ground motion are announced In yield, the NTS continues to be the most advance to news media as a safety pre- suitable area and provides an established cautlon, so that persons In communities facility In a location remote from popu- nearby may avoid being In a hazardous lation centers. The geologic media at the location at the time of detonation. Other explosion sites permit the placement of tests are announced after they have been nuclear devices at sufficient depth for conducted. Some tests with low yields are proper containment and control of radia- not announced. tion. The water table Is relatively deep If cratering experiments are excluded, and water movement Is very slow. Weather all but four (small surface tests) of the conditions permit a year-round testing atmospheric detonations occurred prior to program. the 1958 moratorium. The first full-scale Construction of the Nevada Test Site nuclear detonation, which was designed to facilities began on January 1, 1951. contain all radioactivity underground, was Operation RANGER was the first series of fired at the Nevada Test Site In 1957 In a tests for which the Nevada Test Site was sealed tunnel. Since late 1962, the utilized. The first test was of a one- United States has conducted all of Its kiloton device which was airdropped and nuclear weapons tests underground. detonated on January 27, 1951. In French- A nuclear cratering device, code named man Flat. DANNY BOY, was detonated on Buckboard Mesa After 1951, nuclear test series were on the western portion of the test site In carried out alternately at the Nevada Test 1962 as a military experiment for the Site and at Pacific test locations. Department of Defense. Three of the four Testing at that time was conducted on an small atmospheric (surface) tests men- Intermittent task force basis at both the tioned above were also conducted on the Nevada Test SIte and In the Pacific and flats just to the east of Buckboard Mesa continued In that mode until October, and one, SMALL BOY, was conducted In 1958. Frenchman Flat for the Department of On October 31, 1958, the United States Defense (DOD) In 1962. Thereafter, nu- and the USSR entered Into a voluntary test clear cratering tests were conducted as moratorium which lasted until the USSR part of the peaceful applications (Plow- resumed testing on September 1, 1961. share) program. There have been six such After resuming the U.S. test program at experiments, three of which are mentioned the NTS on September 15, 1961, the Atomic here. The first and largest was SEDAN, a Energy ComMIssion (AEC) revised Its mode 100-kiloton explosion on July 6, 1962, of operations from an Intermittent annual which created a huge crater In the allu- activity to a continuing year-round pro- vium of Area 1O roughly 340 m. across and gram. 98 m. deep. From 1951 untiliearly 1962, all nuclear Nuclear tests have been conducted for a tests at the NTS were under management of variety of reasons: 1) Improvement of the AEC's Albuquerque Operations Office. long-range seismic detection techniques; Because of the significantly Increased 2) conduction of Joint US-UK tests of activities resulting from the resumption United Kingdom devices; 3) development of weapons testing In the fall of 1961, tests for potential peaceful applications the Nevada Operations Office (NV) was (Plowshare); 4) research to collect sclen- established In Las Vegas on March 6, 1962. tific data to better understand the physi- Since the establishment of the Nevada Test cal principles Involved In nuclear explo- Site In 1951 up until the beginning of sions; 5) exploration of new and untried 227 HESS & JACOBSON designs for a given weapon concept; 6) ting Into human food under various con- determining the Interaction between two or taminating situations. more demonstrated components; 7) proof In addition to Its other responsibill- testing of actual warhead designs; 8) ties, beginning In FY 1974, the Nevada conduction of safety tests on certain Operations Office became responsible for designs to test the vulnerability to the custody and administration of the possible accidents; and 9) conduction of geographical area and the facilities at weapons effects tests for the Department the former Nuclear Rocket Development of Defense (for the most part in tunnels) Station (NRDS) (Area 25). The NRDS occu- to determine the effects produced by pied the southwest corner of the Nevada specific weapon outputs upon various Test Site (see Fig. 2). Area 25 contains military systems and components. some S140 million of specialized facili- Although the major effort at the Nevada ties: (1) nuclear reactor/engine/nuclear Test Site has been In nuclear weapons- furnace test stands (known as ETS-1, Test related testing, the activities have Cell C, and Test Cell A); (2) engine Included a variety of both nuclear and maintenance, assembly, and disassembly non-nuclear projects wherein the Depart- building (known as E-MAD); (3) reactor ment of Energy (DOE) laboratories, DOE maintenance, assembly, and disassembly contractors, as well as other government building (known as R-MAD); (4) radioactive agencies and their contractors have taken material storage facility (known as RMSF); advantage of the facilities available, the and (5) other support facilities. climate, the remoteness, and the control- Twenty experimental reactor/nuclear led access of the test site. engine/nuclear furnace tests have been As a part of the program to develop conducted In this area between 1959 and methods for predicting building response termination of program In 1973. to ground motion, two identical four-story In Area 26 (also known as Area 401), reinforced concrete test structures were the Lawrence Livermore National Laboratory constructed In Area 1. Between 1966 and conducted six experimental tests involving 1973, structural response measurements development of a nuclear reactor for a were recorded for 42 underground nuclear ramjet engine as a part of Project Pluto. experiments. These structures were also A radioactive leach field was constructed subjected to a series of low-amplitude adjacent to the disassembly building to dynamic tests for gathering engineering handle radioactive liquids resulting from data on the response of structures to these tests. This field Is some 75 m. by ground motion both with and without non- 80 m. occupying an area of about 6,000 sq. structural Infill walls and partitions. m., and appropriately fenced and marked. By 1973, after sufficient low-amplItude data had been accumulated, high-amplitude, CL IMATE destructive level testing was conducted on one of these structures. These tests were The NTS area lies In the most arld portion carried out In 1974. of Nevada where average rainfall In the A herd of range cattle has been main- valleys range from 7.0 cm. to 15.0 cm. and talned onsite since the mid-1950's and an up to 25 cm. per yr. on the ridges (Wino- experimental dairy farm In Area 15 had grad and Thordarson, 1975). Mean maximum been operated until early 1980's. Levels dally temperatures for the NTS valley of radionuclides In these experimental region In January ranges from 5*C to herds were monitored as part of the rou- 10.5*C and In July ranges from 32-C to tine radiological surveillance program. 41C. Temperatures are 3 to 9- lower on Data from experiments with animals taken the ridges and mesas. Relative humidity from these herds are being used to Improve ranges from 10 to 30 percent In summer and human-dose prediction models and to fur- 20 to 60 percent In winter. nish Information on the effectiveness of Most precipitation on the NTS falls protective actions which may be taken to during the winter and summer months. reduce the amounts of radlonuclides get- Summer convective storms occur over 2-3 228 NTS & AMARGOSA HYDROGEOLOGY sq. km. and are very Intense, In contrast nary sediments are chiefly alluvial valley to winter storms which may cover the fill. The Oligocene and lower Miocene are entire NTS and are less Intense (Winograd composed of freshwater limestones, sand- and Thordarson 197S). stones, and siltstones while upper Miocene rocks are chiefly ash fall tuffs, ash flow GEOLOGICAL SETTING tuffs, and tuff brecclas. Pliocene rocks contain moderately welded to densely The following Geological and Hydrogeologi- welded tuffs with overlying basalt rhyo- cal setting sections were referenced from llte flows. Quaternary sediments are Winograd and Thordarson (1975), which Is chiefly alluvial and fluvIal fanglomer- In part a compilation of other work, and ates, Interbedded with mud flows and lake Fenske (1978). deposits. The NTS lies In a mlogeosynclInal belt of the Cordilieran geosyncline. During HYDROGEOLOGICAL SETTING the Precambrian through the Paleozolc era up to 11,000 m. of sediments were depos- The NTS lies In the most arid region of ited. Except for a few, scattered and the U.S., thus any surface water exists as small Igneous Intrusive masses, sediment- ephemeral streams, however during periods ary Mesozoic rocks are not present on the of extended precipitation, runoff does NTS. In Late Miocene and Early Pllocene collect In Yucca and Frenchman playas the region underwent a period of volcanism forming shallow, temporary lakes. Ground- emplacing 4,000 m. of rocks originating water hydrology on the NTS Is complex and from caldera centers. The Quaternary Is best discussed In the following sec- system Is represented by an erosional tions: the grouping of geologic forma- period resulting In detritus of up to 600 tions In aquifers and aquitards; the m. thick filling In the low lying areas. distribution and saturation extent of the Two major orogenles have deformed the aquifers; and groundwater movement. region. The first occurred In late Meso- Ten hydrogeologic units were designated zoIc, and resulted In major folding and from the geologic formations present In thrust faulting of the Precambrian and the area from well data. By order of Paleozoic rocks. In the middle to late decreasing age they Include the following Cenozoic the second period of deformation (Table 1): lower clastic aqultard; lower occurred causing major block faulting carbonate aquifer; upper clastic aquitard; forming the basin and range structure. upper carbonate aquifer; tuff aqultard; During both orogenles strike slIp faults lava flow aquitard; bedded tuff aquifer; were common with displacements measured up welded tuff aquifer; lava flow aquifer; to several miles long. and the valley fill aquifer. The lower The Precambrian and Paleozolc sediment clastic aqultard Is widely distributed pile Is divided Into 16 formations. The throughout the NTS, Is the hydraulic Precambrian and lower Cambrian are com- basement for carbonate rocks In the re- prised mainly of quartzite Intermixed with glon, and perhaps controls the regional minor amounts of siltstone and dolomite. groundwater movement. The lower carbonate Middle Cambrian to middle Ordovician Is aquifer overlies the lower clastic aqul- dominated by limestones Interbedded with tard and groundwater movement through It some claystones, with the upper Ordovician is controlled primarily by fractures and to upper Devonian consisting of dolomite subsequent solution enlargement. Major and minor amounts of quartzlte. Missis- eastern Nevada springs are fed through sipplan and Pennsylvanlan rocks are large- this aquifer and It Is the only source of ly argillites and limestone respectively. potable water on the NTS where the valley The Cenozoic rocks are divided into two fill aqulfer Is unsaturated. The upper systems, Tertiary and Quaternary, which clastic aquitard Is hydrogeologically contain twelve formations. Volcanics and significant as It separates the upper and associated sedimentary rocks make up the lower carbonate aquifers hydraulically and bulk of Tertiary sediments while Quater- stratigraphically. The upper carbonate 229 HESS £ JACOBSON aquifer consists of Pennsylvanian lime- stone and Is absent from most of the study ranging from 10 to 420 m3d/m. area with exception to western Yucca Flat Distribution and saturated thicknesses where It Is saturated at depths below 600 of the hydrogeologic units discussed are m. Regional groundwater movement Is not htghly variable both laterally and ver- affected or controlled by the upper car- tically In the subsurface due to Tertiary bonate aquifer because of its limited block faulting and pre-Tertlary folding, areal and saturated extent. The tuft faulting, and erosion. The lower car- aquitard separates the Paleozoic and bonate aquifer Is generally saturated Cenozoic aquifers In Frenchman, Yucca, and throughout the area. It Is confined In Jackass Flats. Poor interstitial permea- structurally deep parts of basins and bility and hydraulic connection of frac- unconfined beneath ridges. The tuff aqultard separates the welded tuff aquifer tures probably accounts for the aquItard's ability to control regional groundwater and valley fill aquifers from the lower movement. Most nuclear devices are tested carbonate aquifer In structurally deep In tuffs above the carbonate aquifers portions of Frenchman, Yucca, and Jackass because of Its poor hydraulic conductivl- Flats. In buried pre-Tertlary structural ty, great thickness and wide areal extent. highs the Cenozoic aquifer may be In Little Is known about the lava flow aqul- direct contact with the lower carbonate tard because few drill holes have penetra- aquifer; and water table depth Is not an ted It. Occurrence of the lava flow Important factor for determining extent of aquitard Is limited primarily to the saturation of the lower carbonate aquifers northwest section of Frenchman Flat. The due to great thicknesses of the upper and bedded tuff, welded tuff, and lava flow lower clastic aquitards. aquifers are widely distributed throughout Three types of groundwater movement the NTS, however saturation Is limited to occur In the NTS; movement of perched structurally deep portions of Frenchman, water, Intrabasin movement, and Interbasin Yucca and Jackass Flats. movement of water. Perched water or water Depressions created by post-Pliocene separated from an underlying body of block faulting and subsequent erosion of groundwater by unsaturated rock occurs In ridges producing alluvial-colluvlal fans, ridges and foothills of Frenchman and mud flows and lake bed deposits Is the Yucca Flats In lava flows and tuft aqul- valley fill. Valley fill deposits consist tards. Nine perched springs have been of brown to tan to gray, tuffaceous silts, observed Infthe area. Intrabasin movement sands, and gravels moderately cemented of water Is downward movement or drainage with calcium carbonate. Hard caliche of water from the Quaternary valley fill layers are common In Jackass, Frenchman, aquifer to Paleozolc carbonate aquifers. and Yucca Flats alluvial fan sediments at Evidence of this kind of movement was obtained via test drillIng in Yucca Flat approximately one meter and Is a common cementing material throughout the valley (Moore 1963). Interbasin movement of water Is water which moves laterally fill sediments. Lake bed deposits are chiefly illite, mixed-layered clay miner- beneath basin floors and surrounding als, and montmorillonite, thinly laminated ridges. Water levels In wells penetrating at the surface and becoming more massive the lower carbonate aquifer Indicate a hydraulic gradient from northwest Yucca with depth (Moore and Garber 1962). Thickness of the valley fill Is 570 m. and eastern Frenchmen Flat toward Ash and the Amargosa desert ranging beneath central Yucca Flat, 370 m. beneath Meadows central Frenchman Flat and 320 m. beneath from 0.06 to 1.10 m./km. towards the southwest. Groundwater movement toward central Jackass Flats. The valley fill Is the major aquifer used for water supply In the Ash Meadows discharge area Is con- Frenchman Flat and Is saturated locally In trolled by major strike slip, normal, and structural lows of Yucca and Jackass thrust faults. It Is suggested that the Flats. Pump tests of the valley fill NTS Is hydraulically connected through aquifer yields transmissibility values Interbasin movement to at least ten Inter- 230 NTS & AMARGOSA HYDROGEOLOGY montane valleys and receives significant their extent. The majority of exposed amounts of underflow from northeastern fine-grained sediments range In age from basins (MIfflin, 1968, and Winograd and greater than 30.000 yrs. B.P. to about Thordarson, 1975). less than 5,000 yrs. B.P., with C-14 dates, fossil assemblages, facies changes, ROADLOG and paleosols being used to establish the general age and stratigraphic relation- DAY 1 ships. Depositional environments Indica- Nevada Test Site tive of spring discharge, wet meadows, marshes and perennial stream flow are Mileage Indicated by sedimentary features and 0.0 Department of Energy Building. Las fossil assemblages Incorporated within Vegas, NV. The trip begins from the various units and facles of the deposits. parking lot and proceeds north to the Wet periods are Interpreted as times of Nevada Test Site. Exact directions extensive ground-water discharge, and are not given since this trip cannot other units Indicate dry periods with be duplicated without the permission markedly reduced discharge of ground of the Department of Energy (DOE). water, perhaps similar to current con- ditlons of ground-water discharge I.e., 27.6 STOP 1. NORTHWEST LAS VEGAS VALLEY only a few Isolated spring areas: Tule BADLANDS Springs, Corn Creek Springs, and Indian Spring/Cactus Springs. Evidence has been Exposed Intermittently from southeast of noted by Quade (1982) for secondary cal- the Tule Springs area, about 13 km. to the cite related to former water-table posl- north of Las Vegas, to within 13 km. of tions (the calcareous zones cut across the Mercury turnoff (a total of about 67 stratigraphic horizons when traced from km.) are light colored fine-grain sedl- axial valley exposures to more valley ments of Quaternary age. These contrast marginal exposures). Fossil assemblages sharply with the coarse alluvial fan Include large mammals, mollusks, and In gravels presently being deposited. In some horizons, abundant casts of cicada some areas, such as around and Immediately burrows. north of Tule Springs, the combination of The stratigraphic sequence, Initially Incision by Las Vegas Wash (developed described by Hayes (1967) In the Tule along the axial part of the valley) and Springs area, extends to the fine-grained alluvial fan tributary washes has created deposits to the north, around Corn Creek badland topography on the light colored Flat and the Indian Springs area, studied sediments. On casual examination some of In detail by Quade (1982). Quade combines these deposits appear to be lacustrine and and summarizes the findings as follows: were attributed to pluvial "Lake Las Units A and B are only exposed In the Vegas" by early Investigators. However, lower valley In the vicinity of the Tule as pointed out by Mlfflin and Wheat Spring, the oldest exposed archaeological (1979), paleocilmate models based on the site. Haynes correlates. at least the distribution of well-documented pluvlal upper part of Unit B to the Altonlan lakes In the Great Basin strongly argue Substage of the Midwestern glacial se- against such a large, exclusive lake In quence. Unit B contains greenish pond Las Vegas and Indian Springs Valleys, and clays, black mats, and cicada burrows absence of basin closure and shorelines indicative of moist conditions. Overlying add additional weight to another mode of Unit C represents a shift to dryer condl- origin. The evidence to date points to tions prior to the onset of Late Wisconsin periods of active and extensive ground- pleniglaclal conditions. All these units water discharge associated with the past fall beyond the range of carbon-14 dating. pluvial climates. These sediments have Unit D contains a suite of different been studied by Haynes (1967) and Quade facles Interpreted to represent an exten- (1982) In great detail In several areas of sive marsh-lake complex deposited within 231 W HESS & JACOBSON the time Interval of 30,000 yrs. B.P. to 42.8 Indian Springs -- A small community roughly 16,000 yrs. B.P. On Corn Creek and Air Force Base named after a Flat durIng this time, a broad alluvial perennial spring with a discharge of sand flat surrounded shallow marshy or wet approximately 0.04 m /s. meadow areas In the valley center. Around the Tule Spring archaeological site, a 44.2 Cactus Spring. more continuous body of shallow water was surrounded by a similar alluvial flat. 64.0 Gate to the Nevada Test Site -- Abundant secondary carbonate found In beds Mercury, Nevada of Unit 0 and earlier, was at least part precipitated off of a capillary fringe. 68.0 View of Frenchman Flat. Unit D probably correlates with Early and Mid-Pleniglaclal (25,000 to 15,000 yrs. Traveling north of Mercury, an exposure of B.P.) deposits of Pluvial Lakes Lahontan Paleozolc carbonate rock can be seen in and Bonneville. Red Mountain to the west and the Mercury Unit E Is younger than Unit D and also Ridge to the east. These Cambrian to consists of facles Indicative of perennial Devonian age rocks represent the southern water at or near evidence for gradual extent of the CordIlleran Mlogeosyncline. shrinkage of the marsh-lake complex during The Range Mountains and the Buried Hills the period 13,500 to 7,200 yrs. B.P. This east and northeast of Frenchman Flat are change may have been entirely due to also Paleozolc exposure. The Rock Valley changing climatic conditions or In the fault zone crosses the road south of case of Unit E, possibly It resulted from Frenchman Lake. This fault zone Is a left disruption of basin closure shortly before lateral component of the major right EI deposition. Standing bodies of water lateral, northeast trending component of persisted In the Corn Creek area through the major right lateral, northeast trend- Unit EI time, and they were connected to Ing Walker Lake-Las Vegas Shear zone. The Tule Springs Flat by a marsh-frInged per- Cane Spring fault, northwest of Frenchman ennial stream occasioned by horse, camel, Flat Is a similarly associated left-later- mammoth, and other megafauna. Unit E2 re- al fault system. North and west of the cords persistence of moist conditions to playa are the Massachusetts Mountains and 7,200 yrs. ago in the form of black mats, Mt. Salyer respectively. These mountalns mollusk-rich fluvial deposits, and abun- consist of Tertiary volcanic rocks, most dant burrowing by cicadas. Megafauna were of which are ash flow or ash fall tuffs. probably present In the area Into early The broad, gently sloping basin Is under- Unit E2 time (11,200 - 7,200 yrs. B.P.) laIn by about 400 m. of alluvIal and when the earliest presence of paleoindlans colluvial fill derived from the bordering Is also recorded. mountains. Unbloturbated eollan and fluvial depos- Its testify to the xeric depositional 75.7 STOP 2. RADIONUCLIDE MIGRATION conditions under which Units F and G were PROGRAM (RNM Ditch). formed after about 6,500 yrs. B.P. Llml- This program has been a cooperative ted dissection of fringing areas probably effort between the DRI, LANL, LLNL, began during Unit E2 depositon, whereas USGS. widespread dissection of fine-grained de- posits began after 7,000 yrs. ago. An The Radionuclide Migration Program (RNM) Increase of exotic volcanic detritus (from Is a study of the factors that control the northwestward volcanic terrane of the movement both on and off the Nevada Test NTS area?) In mld-Holocene sediments and Site of radioactivity from underground younger argues for a greater role of nuclear explosions. This Information Is eollan processes In sediment transport applicable to the hydrologic studies during the shift to a dryer and/or warmer related to long-term safety with regard to climate. contamination of water supplies both on- and off-site. 232 NTS & AMARGOSA HYDROGEOLOGY The RNM Program consists of various region was reentered, and a hole (RNM-1) tasks Including experiments at specific was completed to a depth of 370 m. Sam- sites on the NTS, laboratory work related ples were taken to determine the radio- to the field experiments, and mathematical nuclIde distribution between the solid modeling of the field and laboratory material and water at the time the experi- results. The most Intensive Investigation ment was started. Water was then pumped Is currently In progress at the site of from a nearby satellite well (RNM-2s, the Cambric event. actually drilled before RNM-l to avoid Cambric was chosen for a number of contamination), so as to Induce an arti- reasons: 1) the Cambric explosion cavity ficlal gradient sufficient to draw water Is within the NTS Area 5 water-supply from the Cambric cavity and provide an aquifer, and there was particular Interest opportunity for the study of radionuclide In possible contamination of water sup- migration under field conditions. The piles; 2) It was predicted that sufficient pumped water was discharged to a ditch and time had elapsed so that the cavity and conducted to a pond on Frenchman Flat chimney had filled with ground water to where It Is permitted to evaporate and the preshot static water level, 73 m. Infiltrate. above the detonation point. If so, radio- Three types of samples were removed nuclides might be present In the water and from the RNM-1 reentry hole Into the constitute a potential source for migra- Cambric cavity: side cores, pumped water, tion; 3) the Cambric detonation point Is and water with contained gases. Solid only 294 m. below ground surface, and thus samples and water removed from the side the reentry drilling and sampling opera- wall cores from the lower cavity rulon tions would be less difficult and expen- Y5e analyz 11 9 radlochemically for Sr, sive than for more deeply buried tests. Cs, and Pu, and effective distrl- The site In Frenchman Flat Is far enough bution coefficients (ratio of the concen- from the areas of active nuclear testing tration In or on the solid to the concen- so that damage or Interruption of the tratlon In the aqueous phase) were deter- reentry and sampling operations from those mined. These effective distribution activities would3 be unlikely; 4) suffl- coefficients are a measure of both reten- clent tritium ( H or T) was present to tlon In the fused material and sorption. provide an easily measurable tracer for The radlonuclides were found to be almost water from the cavity region; 5) the entirely Incorporated In or on the solid postshot debris also contained plutonium, material. uranium, and fission products whose con- After sidewall core sampling had been centrations In the rubble and ground water completed and the hole had been cleaned, from the cavity and chimney regions could casing was Installed. Beginning at the be measured and compared; 6) the small bottom, the water In five zones was sam- yield (0.73 kt.) was expected to have had pled successively by Isolating the zones little effect on the local hydrology; 7) with Internal packers and perforating the It was Judged that the alluvium constitu- casing. ted a good medium for hydrologic studies Ten years after the test most of the because it was more permeable than tuff radioactivity and the highest concentra- and did not have large fissures or cracks tlons of all radionuclides were still through which the water might selectively found In the region of the original explo flow. slon cavity. No activity was fongd 50 m. The Information from Cambric has con- below the cavity. The measured Kr to T tributed significantly to the understand- ratios for water from the explosion cavity Ing of the radionuclide mobilization and zone were consistent with the relative transport mechanism In the NTS ground- amounts resulting from the Cambric test. water environment. No krypton was observed In water or solid In 1974, two holes were drilled for material from cores taken above the water radionuclide migration studies at the site table. Water from the region of highest of the Cambric test. The Cambric cavity radio-activity at the bottom of the cavity 233 HESS & JACOBSON 90 contained only tritium and Sr at levels since the first observation of tritium, higher than the recommended concentration were reduced to solid residues by evapore- guides for effluent water In uncontrolled tion, and the gamma-ray spectra observed. areas. (Itt 6Phe exception of a very small amount By comparing the measured ratio of each of Ru (concentration < 1 percent of nuclIde detected In the water to the that produced In Cambric), no gamma-emit- tritum In the water with the calculated ting nuclides have been Identified in ratio of the same nuclIde to tritum for these samples. Radlochemical analyses of the Cambric test, an effective overall other water samples for the beta-emitting retention factor, Ed, for each nuclIde nucilde Sr also gave negative results. (ratio of the total activity In or on Chlortne-36 produced by the Cambric solid to the total activity In the eqgeous event has been detected In water samples from RNM-2s using accelerator-based gss 06so) yH estITSed: The lides Sr, Ru, Sb, Cs, and Pu were all spectrometry. The breakthrough of Cl found to have high retention factors, appears to arrive earlier than that of Indicating they are either retained In the tritium, and the peak In the chloride fused debris or highly sorbed on the solid elution clearly occurs before tritium. material, or both. This phenomenon, (called anion exclusion) After completion of the Initial studies where anions arrive earlier than cations described above, the packer between the or neutral species In packed columns, has been observed In two uppermost zones was drilled out and soil chemistry studies the pump was left In place to sample the and column chromatography. water. Since pumping started at the Iodine-129 has been observed In water satellite well, periodic sampling has been pumped from RNM-2s. Although the concen- tratlons are well below the maxlrm per- performed to determine remaining levels of radioactivity. For example, In 1982 after missible concentration of 6 x 10 nCI/mi 635 yrs. of pumping at RNM-2s (6.5 X 10 for drinking water In a controlled area, m of water), the lritium concentration In mobile radlonuclilde specIes of any kind water pumped from RNM-1 had decr ased are of Interest to the general understand- gearly 2,00?3;old. Concentration of Kr, ing of radionuclide trfgport. Relative to the I concentrations Sr, and Cs have also been measured -S and had decreased (Daniels, 1981). measured In RNM1 (1.1 x 10 -5nCd/mI), only The satellite well RNM-2s Is located 91 about one quarter as much I compared to m. from the Cambric explosion cavity. tritim has been recovered at RNM-2s. Pumping was begus In October 1975 at a A DC earth resistivity study along the RNM ditch was conducted In the hopes that rate of about 1 m /min; In October 1937, relative distributions of soil moisture the rate was Increased to about 2.3 m /- Mn. Significant amounts of tritlated could be distinguished. A series of water, signaling arrival of water from the vertical soundings were completed at 3, 15, 25, 30, and 45 m. away from the ditch Cambric cavity region, were ;1nally detec- ted after about 1.44 x 10 m of water had and on both sides of the ditch In order to been pumped from the satellite well. provide a two-dimensional, cross-sectional view of resistivity. These data have been After seven yrs. of pumping, the tritium concentratlon In the pumped water reached converted from apparent resistivity versus a maximum of nearly 3 nCl/ml (the maximum electrode spacing to true resistivity permissible concentration for drinking versus depth and have been contoured on water In a controlled area such as the the basis of electrical conductivity. Two NTS) ang 3S now decreasing. Removal of holes have been drilled for soil moisture samples near the ditch for comparison with 7.1 x 10 m of water from RNM-2s by early October 1982 has also removed 42 percent the resistivity data. of the tritium available from Cambric. A three-dimensional hydraulic and Large volume water samples (0.21 to solute transport numerical modeling study has been recently completed. The goal of 0.90 m ), taken at Intervals from RNM-2s this study was to formulate a conceptual 234 NTS £ AMARGOSA HYDROGEOLOGY model of the RNM site and Incorporate It for the time difference. Secondly, by Into a three dimensional solute transport using the same hydrologic data used for model In order to monitor the migration of tritium, but lowering the retardation tritium and chlorlde-36 through the geolo- factor and reducing the size of the source gic system and to predict the time neces- term, simulated results showed excellent sary to extract all the tritium from the agreement with the field data. This system. Indicated that the conceptual model used Hydrologic data from a nearby well was closely approximates that of the "real used and correlated with that of RNM-1. world". Analysis Indicates that plays type sedl- Although It may be disturbing to find ments dominated the depositional scheme at that tritium will remain In the system In depths of 285-330 m. below the present lower conductivity layers for more than 22 land surface. Hydrologic parameters such years after the Initiation of pumping, as hydraulic conductivity and porosity which Is much longer than RNM-2s break- were estimated from these correlations. through curve data Indicates, evidence DIspersivity values were estimated from Indicates that there Is little danger of analytic solutions. The tritium source fission products migrating any significant term and the tritium exchange radius were distance away from nuclear-produced cavl- determined statistically using a T-test at ties. a 95% confidence level. One major question still remaining The model selected for this study was which will be attempted to be answered titled the Deep Well Disposal Model. It through the ongoing RNM research Is whe- was selected for Its versatility of use ther tritium Is actually being delayed by and Its Incorporation of the third dimen- adsorption, or ton exchange processes, or slon. Symmetry of the radially converging whether Its delay can be explained by self flow field was applied by using 1/4 of the diffusion Into Immobile water regions. It total cylinder of pumping. This scheme will also be beneficial to determine allowed for considerable savings In compu- whether chloride-36 Is experiencing accel- ter memory and execution time. erated movement through the system due to The hydraulic conductivity and porosity anion exclusion or whether it too Is of the cavity region were estimated using actually being delayed by the self diffu- trial and error tests. Once the hydrolo- slon process to some degree. gic scenario was established, It was Of moderate concern Is the possibility necessary to Incorporate a retardation or that tritium may be reentering the system retention factor to get the simulated through a drainage ditch which Is used to breakthrough data to fit the field data. carry pumped water away from the RNM site. Various possibilities for the delay Inclu- If tritium Is being recycled, It would be ded adsorption of tritium, exchange of Interesting to determine how the break- tritium with structural water, and self through curve would be affected If at all. diffusion of tritium Into zones of Immo- Overall, there Is still much continued bile water between pores. work that needs to be done. This project Predictions as to the time needed to has answered many questions on the migra- pump out the tritium mass were determined. tIon of tracers, but an equal amount have Breakthrough curve data didn't represent arisen In conjunction with the findings In the peak concentration within the system this study. In many Instances, average at that particular time. Contour plots values were used; especially In and around showed that significant tritium remained the cavity region where there was limited In the system well after RNM-2s readings data available. However, strong agreement showed little or no tritium remaining. of simulated data to field data Indicates Chlorlde-36 data was analyzed for two that average values within the cavity reasons. First, Its breakthrough time and region are adequate for predictive model- time to peak occurred earlier than that of Ing purposes. Additional Information Is tritium. Results Indicated that anion not needed to accurately simulate the exclusion might have been the major reason field situation. The work In this study 235 HESS & JACOBSON ,does offer Insight Into the long range as a function of position and time. The picture dealing with radionuclide trans- hydraulic conductivities combined with the port and the risks Involved In underground gradients of metric potential allow compu- nuclear testing. tation of volume flux (J), volume per area per unit time, or Darcy velocity, I.e. 78.7 STOP 3. RADIOACTIVE WASTE MANAGEMENT 4 SITE. J K (8 ) The third stop Is the transport study site where h Is the head or metric potential In Area 5 (Fig. 2). The site Is adjacent divided by the product of the density of to the Radioactive Waste Management Site the fluid In the porous medium times the (RWMS) and provides a field laboratory acceleration due to gravity. (Sample where data may be collected which quanti- results are shown In Fig. 3 and are dis- tatively describe the physical processes cussed below). The actual water velocity controlling moisture movement In the upper in the pores, or pore velocity (Vp) Is the 6 m. of the unsaturated zone. The un- Darcy velocity divided by the average saturated flow characteristics of the soil porosity (e), of the medium. In and around the RWMS are being dellnea- The chemistry of the soil water and ted In order to estimate the rate of soil mineralogy determine what nuclide movement, should movement occur, and hence species will be soluble such as uranium In the possible time of arrival of radlonu- a carbonate environment--and which will be clides traveling from the RWMS to the Insoluble--such as uranium In a high water table and possibly to the blosphere. sulfate environment. The cation exchange The relevant unsaturated flow charac- and sorption characteristics of the soil teristics are the pore-volume frequency determine whether the moisture movement In distribution, pore-radius frequency dis- the unsaturated zone may be Inhibited or tribution, porosity, chemical Interactions enhanced, directly affecting the rate of between ImpuritIes In the water and the radionuclide transport. soll-capillary walls, degree of satura- Three Independent studtes to date have tion, and the ambient temperature as well been conducted at the transport study as the variations In these parameters with site. They Include: a simulated 500 year position and time as characterized In precipitation event and construction of a summary form by the metric potential of soil moisture characteristic curve for the the water (0) In the soil. The negative RWMS (Kearl, 1982); descrIbing the soil gradient of the metric potential Is the mineralogy and chemistry with an emghasis driving force for the movement of water in on sorption prgertles of cesium (Cs ) and the vadose zone. strontium (Sr ) (Kautsky, 1984); and de- These parameters are related to the termining the spatial variability of flow velocities In the following way. unsaturated hydraulic conductivity In the From metric potential date It Is possible near surface (Panlan, work In progress). to compute gradients of matric potential To measure temperature and water poten- as a function of position and time. A tial, thermocouple psychrometers were curve fitting technique described by Van burled at various depths on the study Genuchten (1978) was used to calculate a plot. The psychrometer probes contain a curve of unsaturated hydraulic conductivi- copperchromel thermocouple for measuring ty (K(Gs)) as a function of degree of the matric potential (i) In the soil and a saturation (8s). Information used to copper-constantan thermocouple to measure generate this curve are volumetric mois- temperature. The psychrometers were ture content, a site specific moisture connected to a central Instrument shed characteristic curve, and the saturated containing a psychrometer scanner used to hycraulic conductivity of the soil. From automatically record and measure these the degree of saturation data, It Is parameters. A neutron moisture probe was possible, using this curve, to generate used to measure moisture content In the unsaturated hydraulic conductivity values study area. Eight aluminum access tubes 236 NTS & AMARGOSA HYDROGEOLOGY were Installed to a depth of about 6 m. A sisted of estimates of cation exchange neutron moisture gauge containing an capacity, soluble salts, exchangeable americium-241 beryllium source was lowered sodium percentage, pH, and electrical Into the tubes and measured moisture conductance. Textural analyses were content with depth. conducted by the hydrometer method and the The saturated hydraulic conductivity clay fraction was X-rayed In order to was measured In the field with a flooding Identify minerals whose Ion adsorption single ring Infiltrometer and In the characteristics may be unique. laboratory from undisturbed soil cores From the curve of unsaturated hydraulic taken from the study area. conductivity for near-surface soil near The porosity of the soil was estimated the study site as a function of degree of from comparison of the grain size distri- saturation, along with the other para- bution of the soil at the study site to meters described above, a volume flux (J) soils of known porosity discussed In the and a pore velocity (Vp) were computed for literature. the study site. A typical value of pore Representative soil samples were col- velocity for the congitlons of saturation lected at the site In order to character- found to date Is 10 cm/sec or about 1/3 ize the soil and Its adsorptloproperties of a cm/yr. Example results of volume with respect to Cs and Sr . Samples flux as a function of time are shown for were collected using a hand auger and a two depths at one location In Fig. 3. It traller-mounted hollow stem auger at Is seen that near land surface moisture depths ranging from 2 to 9 m. flows toward land surface for most of the Chemical analyses thus far have con- year except for the winter months when the 25 /.9 W -3.1m downlward 0 0 \_;zr t movement TIME (MONTHS) FIGURE 3 Unsaturated groundwater flow velocity as a function of time at two respresentative depths. 237 HESS £ JACOBSON trend Is downward. meters measured were discharge, gross chemistry and environmental Isotopes. FLOOD HAZARD EVALUATION These data are used to analyze re- charge to shallow ground water in a Hydrologic analyses In general and flood semi-arid environment. This Is used hazard evaluations In particular are to resolve travel times and flow difficult to perform In desert and arid velocities in. a fractured medlum regions. In such areas stream gaging (Jacobson and Hess, 1984). It ap- records are usually of short length, when pears that the residence time for they exist, and are usually composed of some of the discharging water In the many low outliers with only a few meaning- unsaturated zone Is approximately one ful values. With these data limitations, month and approximately six months In the traditional methods of peak flood flow the saturated zone. estimation are not applicable and regional peak flood flow regression equations or Cane Spring Is located at 36-47'56" N. rainfall runoff models are frequently Lat., 116-05'42" W. Long. at an elevation used. of 1238 m. on the northeast trending Cane Another difficulty In evaluating poten- Spring Fault Zone. The spring lies low on tial flood hazards to facilities In arid a hillside about 0.9 km. south from a regions occurs when the facility Is sited southward bend In Cane Spring Road at a on one or more alluvial fans. From a point roughly 10 km. west from Its Junc- quantitative viewpoint, the formation of ture with Mercury Highway. these Important geological features and Soils In the area are poorly developed the movement of flood flows across them In alluvial materials, which derive from are very poorly understood. the surrounding high ground composed of The Radioactive Waste Management Site Miocene aged volcanics of the Wahmonle and (RWMS) is located at the Junction of major Salyer Formations (Poole, Elston, and Carr alluvial fans to the east and west, with 1965). The Wahmonle In the spring vicini- several smaller fans merging from the ty Is primarily composed of dacite and north; Fig. 4. The conclusion Is that the rhyodacite lava flows containing quartz, RWMS Is likely to be hit several times plagloclase feldspars, pyroxene, horn- during an assumed design life of 100 yrs. blende, blotite, and magnetite. The by flash flood events of significant Salyer here Is composed of lithic brec- magnitude. This conclusion was arrived at clas, breccla flows, tuffs and tuff brec- by using regional peak flood flow equa- clas, and sandstones of similar minera- tions developed by the U.S. Geological logy. The bedrock In the area is highly Survey and various hypotheses regarding fractured and faulted, with numerous flood processes on alluvial fans. smaller faults terminating In the Cane Although this analysis Is subject to a Spring Fault Zone, mostly from the south. number of serious limitations, the con- Water at the sprIng collects In an cluslon was substantiated by the fact that edit, hand dug roughly 15 m. southward the RWMS Is located on a number of allu- into the hillside at a shallow angle. The vial fans which were formed by erosional edit pool contains an estimated 21 cu. m. processes that are still active. of water. The water, audibly trickling into the pool near the back, currently 83.1 Going up the alluvial fan to your discharges through a gravity-feed pipe left Is the road to Jackass Flat, under a small earthen dam at the mouth of Fortymile Canyon and Yucca Mountain. the edit. However, large trees and wet Ten km. up this fan Is Cane Spring, soils (the latter observed In July of the site of Investigations of the 1980), some 50 m. from the edit at the behavior of a shallow perched ground- same elevation, Indicate local ground- water system. water discharges other than that repre- Time-serles data have been collec- sented by the edit pool. ted over the past 4 yrs. The para- 238 dommom NTS & AMARGOSA HYDROGEOLOGY ( 7' I I ¼ - . J 7-.- \, '7 . '7 I '7-. V -\V \. , \ N ) NJ N \*-.. '7.. 7. 7 '7 WAY ERSNUO...j2 . / -7-. N ". \ '7 I( )~~~~~~ 7- N I' ) - N S.' * __ -. \WAYERS 4EO 6 ~ ~~~~/ N\ 0 -7' -- VI V I 'I ! / I- . / .. . . N .7'' I dA.ae . ' I * SAkE'"... -. -. A 'I S. i 7-' SC A RP CANYON .. . .. ..-. F A N Z 1: ! l / \I/ /. N I I~~~~~~~~~~~~~~~~~~N~~~~~~~~~~~~~~~~~~~~~~~ f,, II Lake I *S 0 W1 Ftenchmea I . . 0 C .S seALs FIGURE 4 Location of RWMS relative to the surrounding alluvial fans 239 HESS C JACOBSON 100.0 Intersection of TIppipah Highway and has been made, and the horizons that Pahute Mesa Roads. To the west of several sizes and species of plants uti- this Intersection Is the site of the lize as water sources Identified. Com- wash Infiltration study. bined, the resulting data will Indicate the net direction, magnitude, and charac- WATER MOVEMENT IN DESERT DRY WASHES ter of water movement In this micro-en- vironment through time, thus establishing Recent Isotopic and water chemistry stud- a baseline for further studies of epheme- les Indicate that groundwater recharge In ral wash recharge on a larger scale. arid zones occurs via ephemeral wash channels after flood events. This study 105.4 To the right, down the alluvial fan assesses such recharge potential by exam- Is hydrologic test well Ue2ce. Ining the soll-water-climate-vegetation Interactions In the upper 9 m. of a wash 109.5 STOP 4. AREA 12 CAMP -- Lunch. channel, as the primary water Infiltration restraints of evaporation and transpira- 111.6 View of Rainier Mesa and Tunnel tion by vegetation are most Intense In Portals. this region. Based on the geomorphic and geologic 113.0 STOP 5. VIEW OF RAINIER MESA AND characteristics of the wash and Its drain- YUCCA VALLEY. age basin, and the availability of past precipitation, psychrometer and electrical The tunnels Into the tuffs of Rainier Mesa resistivity survey data, of a particularly afford a unique opportunity to Intercept flood prone wash above the NTS Area 1 unsaturated flow halfway down to the water Shaker Plant was chosen. The study site table. This allows Investigations of elevation Is about 1525 m. and the average recharge mechanisms and the movement of annual precipitation Is 20 cm. After water through thick unsaturated zones. doing a shallow seismic survey so as to Precipitation amounts, chemistry and avoid callche underlain areas, 9 m. holes Isotopic composition are measured on the were drilled in a well-defined alluvial top of the mesa at several points. Addl- channel and an Interchannel area (as a tionally, soil moisture contents and chem- control), each Instrumented with 2 psy- istry are also determined. These data are chrometers (which measure temperature and then compared to discharge, water quality soil water potential) and a soil gas and Isotopic composition of tunnel waters. collection port (to collect soil water This allows the calculation of residence vapor) at 0.5, 1.0, 2.6, 4.2, 5.8, 7.4, times and probable flow paths. and 9.0 m. Aluminum cased neutron probe The geology of Rainier Mesa affects access holes were Installed adjacent to both the groundwater flow and the geo- each of these to allow determination of chemical reactions that occur within the water content. To collect water samples tuffs. Minerals found In the various independent of the gas collection ports, strata of the mesa show those constituents suction lysimeters were Installed at 0.5 which might be at saturation level within and 1 m. depths. Fig. 5 Is a cross-sec- the groundwater. The groundwater flow and tion showing Instrumentation In the wash mineral precipitation govern the chemistry site. of waters collected from the tuffs of the A soil moisture potential, water con- mesa. tent, and temperature profile of all of As seen from Yucca Flat, Rainier Mesa the holes Is made weekly. Soil water and Is composed of a succession of nearly vegetation samples have been collected parallel stratigraphic units with a slight monthly and analyzed for oxygen and hydro- dip of 10 to 25- to the west. Thicknesses gen Isotope ratios. Through comparison of these strata vary considerably, depen- with collected precipitation and runoff, a dent upon location. Measurements have calculation of the evaporative processes been made In numerous drill holes, In acting on the water during Infiltration tunnels penetrating the mesa, and In 240 NTS £ AMARGOSA HYDROGEOLOGY Cross-Section of Wash Site Psychrometers and Ga. Sampling Ports Neutron Probe Access Pipee Lymeitoers Flood Water I Collection Bottles Z)111 I I Ground Surface t 4 Gas Tube Heeter I E 4- e K a- i I a1- I0- FIGURE 5 Instrumentation schematic of the Wash Site exposed areas on the sides of the mesa. A fractures, Joints, or small faults (Fairer compilatIon of these data Is given In et Table 1. al. 1979). The mesa has been modified in one location by a series of Faulting and fracturing of the volcanic broad shallow anticlines and synclines tuffs are found in many locations through- (Hansen, et al., 1963). out Rainier Mesa; at times these faults Abundant fractures in Rainier Mesa extend only through one or several strati- are most visible In the welded and partially graphic units. Many of the faults visible welded tuffs, where they were created by on the surface of the mesa are Indicated cooling as well as structural deforma- on the map by Gibbons et al., (1963). The tions. Fractures are also present In the surface Is extensively scarred by ero- zeolItized tuffs, although to a lesser sional gullies controlled by cooling extent. The friable nature of the vitric- 241 HESS & JACOBSON TABLE 1. Stratigraphic and hydrogeologic units at Nevada Test Site and vicinity (After Winograd and Thordarson, 1975) p q - - - Maxwnrn -mgimr ww mym W-muuiw cherewmvm and-, ' at (few WrE -N-r'm ~~-~g Ko~o~ I Valley 61Alluvial fsaa.fu. 200 Vllyfl C ftabuminbdicy "mni ftcm 1.0W to Tarafry 1'tsaumam. Ifiamoaram. taebabd. I I mqO r900 Vd LUzaeatr.M cowdimt @fWWIISCtSAL and and mudilm depa I PwumbdltAEY inugmqftwm I to0 pnd par aq ft: PboiN. Js t*rjt5d onl beet tutrlydee pagmsat Yoms Flat Nad ?aenhuaFNL Summiat Kani Mm Bmasat fIoss dim". usd water mayma CamUalld by gn y(tooling) mid Rhrfimo ' , h-i'lo&ML I mm~dmyhactuemad hly b rabble ba IMIY Bsal a(Skoll B ymit110,m dMtam PlM Ammomna Tanks Ash-flaw tuff modratuay I ~ ~~ ~ ~~s-altif ths.Water mowvement cossualld by prinmay (eoodin) and a- tBine 1M." Ash~flow tuff notrwlded M0 aodz oa adaaywde ptartof a-dow I Member to darsemi wilc this t luff: oagpaaVW tmmrirmmbtltyft. lig bMy and IL ssb~~mall tuff at beass odd-m. amssblmO10.WP4,UtabiICIuneiAde aomtymahnd flvs~~~auv Ash-11ow tnt mowelddd 300-l dcey~mmtta CaY UMbe to dornety wadded., Uki2gp l n y m la ______mb-t~all tuff seam bow. ~ tOf A TogpmakSwnng Aabhfaw tmMl wasswedda 900 Member ,,,dyedetin I addad tom Asb..&l1 tuff NWandfuwuiy LOW Ccd~itaofddwf trasmissibility ingua fron 20 to (in(sLk Unit "Worked tuff equiller 1.00Wgad per ft samuzemd only-bomwmi sawn- & ~~~~~~~~~~~~~~~~~~~~tuaallydeep"m Pamof Yuuma FIAaracbsan MLt.and Jackain Flats Occna, locally bmww ama- flow toff embearsi of Paintbumab Tut and bmw ______G mrn.Canyan M oember at India Tram F ajats ias. LWvaDaW and istiiam tavemtum Water momment cotrollted by poouly mannctad fret. tuf amd braedia- -ml S"U-d. tovm: Mnt-awm" vaorty amn P-batmaascy begfigi- hpsa. llvmsed. de. amiscimat at tsrninbuLSMty acmaced low tm all a t ona LWP ae Fin . bo ahaPIan ame Wao Fromadam ASk-tal tuff M10 sandatone. sad tuft brecnus. all intarbdded: Eaau cmimany aimym Or sooibe; Bseads flw. li~bl bay- . 200 aim.and tuff breacts i-. tIndad"e with mb-tall Tordery blm Smiyer~~mma~e tufm. madaaase. silt- enmmo myelmyaro Ggicaru mina AmA-flaw tuft. denauly 1w wadded- Tub AMM alaUbar, Ash-dow MM moswalded 100 tma waressai Aab-tak~l tit,momslead to. LO0W aemaw~ddd mbh-fla tWit. tuffaaaemaa mand. Cked~chasm a(truemmastiouity ftmagtea 1000toS Man". Witatume. and w LUrt istamnzal Porosity a ba~h 40 pa- ciaymmto all mmurneed CMnt bait urteratital parmmabaclly a nae~gbl. texte to Sx10-6 gpd per aq a): ommg topo adw tuaalt o day bydnull.i amenaction at frwtcurMa iataseItial pWra~biity Probably amatula moon" pound- __ _ _ ~~~~mnor rkolt and Taff waler awammitc -n tmanor quancibs t oWater bomosiat. lml.ae beneath Lactinlla daninag vilwm fully saturatad - osAastraucturally davowa Pamt ot Yucca Fla reacitman FILat snd Jackass Flats; GOmam Canyon and Tub StrIg Mambarm ot In-ian Trail Rbroaft aft nd Rbyalits. -aew and Fajatia May lainly be Gqtiar Annwtbatu Ymst r~fc~bad of ,1 flow, amb-tal es FIlat Camoie. viufbawada. nad- tageoua sandatoum; tuff and mandum co- manly uelaay at ueattlli. 1Tafaetoinem AiMb-do tntm% nedd 3 to puitty welded, (a. mbatdded with "ashti Worm~~~~~~da r ni and tocnekaaPm ampuing Tuffacmmis mdandso and 1.400 OU~~~~aame m~~~~sitlatone.eisysafteum thelb-wraer Uinaatamm mad congloemrate; Iu OPN= Macrit famosinay Clayey. ______ml orc.t a lwm a OLWM Ham Sprp feuma raab-wawtar limestone. COaOEWWA MMt -a. - ______242 NTS & AMARGOSA HYDROGEOLOGY (Jszto"ui nonbi Cretaceous to Granitic stocks Granodioiut and quarts (A minor Complexly fractured but nearly impermeable. Parmua monsonite in stocks. aquoitard dike. &no sills. pfrmian aNd rippipab Limestne Limestone. 3.600 Upper Complexly fractured aquifer: coefficient of Psylvanis carbonate trmisaibility estated in range from 1000 to aquifer 100.000 gpd per ft. intrcrystalline poroeity and p rmeability neliibl. saturated only beneath waon tlxir of Yucca Flat. Miesiepposis Elsan Formation Argillite. quartite. n- 900 Upper Complexly fatud but neatly impermeablet o. and Devsusa glomerate. corglomer- clastic slliiemnt od transmiesibility estimatud I_ tan 600 ita. lim n quttard pd per ftR intr titia l permeabity negligible but owing to poor hydrulie connection of fractures probably controla ground-waer movement: saturated ony beth _te Yucca Fl"t and Jacka Flats. Upper DevilsGateLimestone Limestone. dolomite. >1.180 Dev _ minorquartzite. !ltddla Nevada Formation Dolomite. > 1.52 DeOnian d Undiffereciated Dolomite. 1.415 Siluran Upper Ely Springn Dolomite Dolomite l0b Eureka Quartziue Quartite. minor lim. 340 Middle ston. Ordovician Antelope Valley Limestone and silty 1.530 07deri? - - UnLimesnes limestone. ini= NinemieFormation ClzyatoNe and limestone. Complexly frctured aquifer hicds spplies mo LAMwer NimieFrmt] Caytnte dand.lmsoe transJmissibiiityspruigethroughsout rarigi eastern hrc Nevadst1.000 to lcoedlic2ent COOC0lDjgpd of ~~~~~~~~~~inueroLdLodr 1 W Goodusa lsinsatonelimestone. - per ft: intarastaine'i porostyand prmabisi i Lim im >900 carbonate~~~~~Lower negligible solution caverst an present locally but aquifer r ioi u ur mo t Lacontrolled by Nopak Fornation Dolomite. limestone. t.07 fracture transmiaeibiiity saturwaed beraath mucs Smoky Uenbr _f Std rs Upperupper ~Halfpint Member Limestone.silty limestone. dolomite.05y 15 a Dunderbert Shale Shale, minor limetone. Member Bonanza King Formation Limestone. dolomite. Banded Mountain minor siltatone. 2.440 Member Cambrian Papoose LAMiMember Limetone. dolomite. Middle minor siltston.. 2.16t Carrar Formation Siltatone limestone. in. 100 tsbdded Upper 1.050 feet predominantly limesooi lower,950 fest 9g0 predominantly siltatca. Lower Zabriskie Quartoite Quarezite. Complexly fractured but nearly impermeable: supplies no major springs; coefficsent of Wood Canvon Formation Qutite. silttone. shale. 2.85 Lower iranamisaibility le than 1.000 gpd per ft: in. minor dolomite, clatic teratitii poroity and permeability is negligible. SquitaiP but probably conti reginal ground-water rmov. Stirling Quarboite Quartzite. siltatoms. .410Mont owing to poor hyrui oncino rc Precambrian turer saturated beneath most of study area. JohnnieFormation Quartzite. sandstone. 1200 siltatone. minor lime. stone and dolomite. 'Coafrciat of transmissibility hue the unita galls. per day *1Thethree Miocene sequences ccur in separate parts of the I'he Noonday?) Dolomite. hich undlerlie the Johanne per foot Igpd per ftl width ot aquifer coefficient of region. Age corrations between them ant uncertain. They are Formatin. is considered per of th r elastic aqusiard. permebsity has the unite galons per day per square foot (gpd pl acd vertically in table to sane pace. per sq I of aquifer. 243 HESS & JACOBSON bedded tuffs suggests that open fractures Is more homogeneous than the physical preserved In these rocks. are rarely composition. Slica concentrations vary Fractures observed In outcrops of the only slightly between the different units friable-vitric tuffs are filled with a of Rainier Mesa and cation concentrations, clayey gouge-Iike deposit (Thordarson, although more varied, remain within the 1965). same order of magnitude. The tuffs have been divided Into three types based upon their mineralogy and PRECIPITATION NETWORK composition. In order to provide baseline Input data 1) The zeolitic-bedded tuffs are found for many of the hydrogeologic Investiga- In Tunnel Beds 1 through 4 and portions of tions on the NTS, a precipitation network the Paintbrush Tuff. They were deposited of 16 stations has been set up to collect by the fall of volcanic ash, which con- precipitation samples for Isotopic compo- sisted predominantly of pumice and glass sitlon (Fig. 2). These are located around shards (Thordarson, 1965). This material the NTS at different elevations. They are was later massively altered, predominantly designed to suppress evaporation. Associ- to the zeolltic minerals cilnoptilolite, ated with each gauge Is a suction lysl- mordenite, and analcime. Minor amounts of meter for sampling soil waters or gases. clay minerals as well as some silica and The groundwater flow regimes on NTS hematite are also present (Thordarson, have been studied for approximately 20 1965). Non-zeolitic constituents general- yrs. and are still not well understood. A ly make up 5 to 30 percent of the zeolltic large part of the problem Is the low bedded tuft. These are small crystals of density of wells drilled for hydrologic quartz, feldspar, blotite, and dense purposes and still a smaller number from lithic fragments. which good quality water chemistry samples 2) The friable-bedded tuffs dominate In may be obtained. At the present time the Tunnel Beds, Unit 5 and most of the Paint- well density with pumps Is one well per brush Tuff. They were deposited as an 200 sq. km. ash-fall, but, In contrast to the zeolitic The groundwater potentiometric surface tuffs, the pumice and glass shards have Indicates the flow on NTS should be gener- undergone only minor alteration. The ally south with several major deviations absence of zeolites and other cementing of flow. One major feature on the poten- materials make these tuffs very friable. tiometric surface Is a trough In the Yucca Only small quantities of quartz, quartz- and Frenchman Flat area. Waters recharged lte, K-feldspar and plagloclase have been or flowing under the NTS are generally noted In Tunnel Beds, Unit 5 and the believed to discharge In the Amargosa Paintbrush Tuff. Desert/Ash Meadows area, which are west 3) The welded and partially welded and south of NTS. tuffs compose the Rainier Mesa member of the Timber Mountain Tuft, the Stockade 126.0 STOP 6. SEDAN CRATER. Wash and Tiva Canyon members of the Paint- brush Tuft, the Grouse Canyon and Tub The crater was formed by a 100 kt. device Spring members of the Belted Range Tuff, as part of the Plowshare Program July 6, and portions of the Crater Flat Tuff. 1962. It Is 340 m. across and 98 m. deep. They were deposited as ash flows and welded together by their own heat and 135.5 Drill yard on the left. weight. Some of the units have friable, partially welded or nonwelded bases that 140.0 Driving through east Yucca Valley grade Indistinctly Into welded tuffs. where collapsed craters can be seen Sanidine, andesine, blotite, anorthoclase, on either side. DRI and USGS have quartz and plagloclase have been reported been studying the Infilration of to occur locally In these tuffs (Hansen, water In the craters. They may et al., 1963; Emerick, 1966). represent Important locations of The chemical composition of the tuffs groundwater recharge. Geophysics 244 NTS X AMARGOSA HYDROGEOLOGY and soil moisture measurements have In filters) structures and strati- been used to track the movement of graphy of the Tertiary and later soil water as a function of crater valley fill may be seen. Near this size and age. point Ash Spring discharges water of very different quality from the 145.6 STOP 7. YUCCA LAKE. water In the valley of the Amargosa Yucca Lake Is a typical "recharging" River to the west or from that In playa. It is 14.25 km In area. Ash Meadows to the east. The flow The depth to groundwater is greater system here exhibits a relatively than 450 a. It receives approxi- high "ridge" with discharge points mately 200 mm/yr precipitation with several feet higher than Is dis- a potential evaporation of 1,700 charged either to the east or west. mm/yr. Several times a year the This ridge Is obviously closely playa Is covered with a shallow lake related to the complexly faulted and receiving runoff from adjacent folded Tertiary valley fill In this areas. area. The groundwater ridge Is obviously accentuated by low water 175.7 Mercury, Nevada. levels resulting from evapotrans- piratlon of ground water to the east 202.0 Lathrop Wells, Nevada -- Note large In Carson Slough. sand dunes to the left (south) of the highway. To the right Is Yucca 281.4 STOP 8. CRYSTAL POOL. Mountain, the site of a proposed Spring (Turn right through gate to High Level Nuclear Waste Repository. spring). 231.0 Beatty, Nevada -- Spend the night A typical large spring representing dis- near U.S. Ecology - a low level charge from the Ash Meadows ground-water nuclear waste disposal site. system. Temperature of the water Is 31C with an electrical conductivity 3 f 650 mhos and a discharge of 15,700 m /day. DAY 2 Total spring discharge from the aquifer 3at SOUTHERN AMARGOSA DESERT Ash Meadows Is approximately 58,000 m /- day. The average carbon-14 content of The following field trip to the Southern Crystal Pool Is 11.1% modern while the Amargosa Desert Is a modification of ones average for the other springs In the area run during the March 1974 Geological is 2.3% modern (Winograd and Pearson, Society of America Cordilieran Section 1976). Meeting, Las Vegas, Nevada (Naff, et. al., 1974) and the September 1979 Sixth Con- 282.3 Turn right on County Road. ference on Karst Hydrogeology and Speleo- logy. Mileages are approximate. 284.8 Turn left. 231.0 Beatty, Nevada 286.2 Turn left. U.S. Ecology Yucca Mountain 286.3 STOP 9. DEVIL'S HOLE. 260.0 Lathrop Wells, Nevada -- Turn right This location demonstrates the role of on State Route 373. reservoir mechanics In relation to the problem of preserving an endangered spe- 275.3 Turn left onto paved road - turns to cies, the Desert Pupfish. Pumping of the gravel. alluvial aquifer for agricultural purposes lowered the water level In Devil's Hole, a 276.5 Clay Camp. In the abandoned clay karst fenster. Water temperature Is pits (the clay mined here was used 33.5*C. 245 , I , , HESS £ JACOBSON Is cut Into the Moenkopl Shale. The 286.4 Turn right. Shinarump Conglomerate forms the small dark hogback on the west side of the 287.5 Turn left. valley. It Is overlain successively by the Chinle (purplish and red beds), the 288.0 Turn left. Kayenta, and the cliff-forming Aztec Sandstone. The Aztec, In turn, Is over- 289.7 STOP 10. POINT OF ROCKS SPRING -- lain by Paleozolc limestones which were Lunch. thrust over the Aztec In Laramide time (Keystone and Red Rock thrust faults). Another spring discharging from the Ash Breccia believed to be the sole of the Meadows groundwater syst3m. The discharge thrust Is draped over the Aztec and under- Is approximately 8,400 m /day with a temp- lying rocks In a few places. The Keystone erature of 33C and an electrical conduc- and related thrusts did not displace the tivity of 660 Uemhos. crust as much on the southwest side of Las Vegas Valley as the Muddy Mountain and 306.2 Continue to the east on road. related faults did on the northeast side. intersection of Bellvista Road and This resulted In a shear zone now occupied Leslie Street. Turn right. by Las Vegas Valley. This shear zone extends under the Tertiary volcanic rocks 307.2 Turn left on to Mesquite. of the River Mountains and McCullough Range to the south. It extends northward 309.6 Turn right on to Route 160. beyond Indian Springs, and Is believed to be associated with the Walker Lane, pos- 312.4 Pahrump Valley. sibly Intersecting the latter. 324.2 Road to the left goes to Trout 362.1 STOP 12. REDROCK MUSEUM. Canyon. Several caves are In the canyon Including Deer Spring Cave. 375.4 STOP 13. Las Vegas Valley Water District Well Field. 332.0 Road to the right goes to Tacopa Hot Springs. This Is the West Charleston well field, an area (about 1/2 section) which has been 348.1 Mountain Springs Summit. chief source of the supply of groundwater for Las Vegas Valley. The site of Big 348.8 Road to left goes to Potosi Mine and Spring was at the north end of the well Pinnacle Cave In the Potosi Moun- field about 0.5 km. east of here. It toins. supplied the city for many years, until pumping from wells reduced the head and 349.5 Cross the Keystone Thrust fault In the spring stopped flowing (about 1947). which Jurassic Aztec Sandstone has Note the scarp at this location, one of been thrust over the Paleozoic the several scarps believed to be the carbonates. result of differential compaction of the valley-fill materials. Another (possibly 352.7 Gypsum Mine on the right. two?) such scarp occurs west of here, and the largest scarp occurs a few kilometers 361.1 STOP 11. REDROCK OVERLOOK. to the east In the eastern part of Las The general strotigraphy and struc- Vegas and the western part of North Las ture of the Las Vegas area may be Vegas. All of these scarps are aligned observed from this location. north-south and veer to the northeast of Las Vegas. Relationship to tectonic Bedrock here consists of Permian Kalbab features In the bedrock has been searched Limestone very close to the Permian-Trlas- for, but none has ever been discovered. sic boundary. Looking westward the valley Since the scarps occur where the Ilthology 246 NTS & AMARGOSA HYDROGEOLOGY changes from predominantly gravel and sand National Laboratory, Dept. LA-9192-PR. on the west to predominantly silt and clay Emerick, W. L., 1966, Physical Properties on the east they are interpreted as dif- of Volcanic Rocks, Rainier Mesa and ferential compaction features. Evidence Vicinity, Nevada Test Site: USGS Tech- of subsidence as a result of withdrawal of nical Letter: Area 12-18. groundwater has been observed along most Fairer, G. M., Townsend, D. R., Carroll, of the scarps. Cracking at the surface, R. D., Cunningham, M. J., Muller, D. vertical extrusion of well casings, dis- C., Healey 0. L., and Ellis, W. L., placed water mains, and displaced and 1979, U.S. Geological Survey Investiga- distorted structures, all attest to such tion In Connection with the Mighty Epic subsidence. Correlation between fluctua- Event, U12n.10 Tunnel, Nevada Test tions In withdrawal of water and subsi- Site: USGS 474-228. dence has been documented. Fenske, P. R., 1978, Interaqulfer Leakage The Las Vegas Valley groundwater system Through Uncored Boreholes Penetrations, roughly occupies the watershed area of Las Yucca Valley, Nevada Test Site: Desert Vegas Valley but may be connected hydraul- Research Institute, NV, Report Series ically with systems contiguous to It, 43013, University of Nevada, Reno. especially to the north (Ash Meadows Hayes, C. V., 1967, Quaternary geology of system), and to the northeast (White River the Tule Springs Area, Clark County, Valley system). Little Is known of the Nev., Nev. State Museum Anthro. Papers deeper part of the system (below about 600 No. 13, 104 p. m.) since only a few oil, brine, and Jacobson, Roger L., and Hess, John W., geothermal test wells have been drilled. 1984, Time Series Analysis of Geocheml- The deepest reported test hole Is approxi- cal and Isotope Data In Semi-arid mately 2600 m. Regions, Geochemical Symposium in Banff, Canada, June 22-26, 1984. 379.7 Return to the Las Vegas Airport. Kautsky, M., 1984, Sorption of Cesium and Trip ends. Strontium by Arid Region Desert Soil. Water Resources Ctr., Desert Research ACKNOWLEDGEMENTS Institute, University of Nevada System, Reno. The leaders would like to thank the fol- Kearl, P. M., 1982, Water Transport In lowing people who contributed parts of Desert Alluvial Soil. Water Resources this guidebook: Clinton M. Case for a Ctr., University of Nevada System, discussion on the Radioactive Waste Man- Reno, Pub. No. 45024, 130 p. agement Site; Paul R. Fenske for the Mifflin, M. 0., 1968, Delination of Historical Background and part of the RNM groundwater flow systems In Nevada, program; Richard H. French for contrIbut- Desert Research Institute, CWRR, Tech. ing the Flood Hazard evaluation; Martin D. Rpt., Series H-W, Publ. 4, 111 p. Mifflin for writing the section on the Las . and Wheat, M. M., 1979, Pluvial Vegas Valley Badlands; Stephen W. Wheat- Lakes and Estimated Pluvial Climates of craft for the discussions of the RNM Nevada, Nevada Bureau of Mines and program and the- many graduate students Geology Bulletin 94, University of Including Mark S. Henne, Donald S. Hansen, Nev., Reno. Carol J. Boughton and Sarah L. Raker who Moore, J. E., and Garber, M. S., 1962, have contributed M.S. Theses on the NTS Ground-water test well B, Nevada Test through the years. Site, Nye County, Nevada: U.S. Geol. Survey TEI-836, Open File Report, 73 p. REFERENCES _ and Garber, M. S., 1962, Ground- water test well B, Nevada Test Site, Daniels, W. R., Ed., 1981, Laboratory and Nye County, Nevada: U.S. Geol. Survey Field Studies Related to the Radionu- TEI-808, Open File Rept., 39 p. cilde Migration Project, October 1, Naff, R. L., Maxey, G. B., and Kaufmann, 1979 - September 30, 1980: Los Alamos R. F., 1974, Interbasin Ground-Water 247 S 'I r HESS & JACOBSON Flow In Southera Nevada, Nevada Bureau Winograd, 1. J., and Thordarson, W., 1975. of Mines and Geology Rpt. 20, 28 p. Hydrogeologic and Hydrochemical Frame- Panlan, T., 1984, Master's Thesis In work, South-Central Great Basin, Neva- progress, University of Nevada, Reno. da-Callfornia, with Special Reference Poole, F. G., Elston, D. P., and Carr, W. to the Nevada Test Site, U.S. Geol. J., 1965. Geologic map of the Cane Survey Prof. Paper 712C, 126 p. Springs Quadrangle, Nye County, NV, . and Pearson, F. J., 1976, MaJor U.S. Geol. Survey, Geological Quad. Map Carbon-14 Anomaly In a Regional Carbo- EQ455. nate Aquifer: Possible Evidence for Quade, J., 1982, Quaternary Geology of the Megascale Channeling, South Central Corn Creek Springs Area, Clark County, Great Basin, Water Resources Research Nevada, Tucson, University of Arizona 12:6, p. 1125-1143. MS Thesis, 130 p. Thordarson, W., 1965, Perched Ground Water in Zeolitized-Bedded Tuff, Rainier Mesa and Vicinity, Nevada Test Site, Nevada, USGS TEI-862, 90 p. Van Genuchten, R., 1978, Calculating the Unsaturated Hydraulic Conductivity with a New Closed-Form Analytical Model, Dept. of Civil Engineering, Princeton Univ., New Jersey. 248 1I