Holocene Scarp on the Sawtooth Fault, Central Idaho, USA, Documented Through Lidar Topographic Analysis

Holocene scarp on the Sawtooth fault, central Idaho, USA, documented through lidar topographic analysis

Glenn D. Thackray*, David W. Rodgers, and David Streutker Department of Geosciences, Idaho State University, Pocatello, Idaho 83209, USA

ABSTRACT surface from raw point data, and rasterizes High-resolution lidar data reveal a prominent latest Pleistocene–Holocene scarp on the those data to resolutions as fi ne as 1 m. Sawtooth fault (central Idaho, United States). The fault scarp marks 55–65 km of the range In the areas of lidar coverage, we analyzed the front, and may comprise two segments. The scarp is 4–9 m high in latest Pleistocene glacial bare-earth DEM data sets and associated digital landforms (11–14 ka) and 2–3 m high in Holocene alluvial landforms, implying 2–3 postglacial hillshade images, SPOT satellite imagery, aerial rupture events. Patterns of fault scarp continuity, coupled with existing gravity data, suggest photographs, and surfi cial geologic maps in that active faulting may have migrated northward during Pleistocene time. Detailed compari- ArcGIS 9.2 (ESRI, 2006). We extracted topo- sons of raw lidar digital elevation models (DEMs), bare-earth lidar DEMs, and fi eld surveys graphic profi les across the fault scarp from the indicate that the bare-earth lidar data document the fault scarp morphology accurately and raw (vegetated) and bare-earth lidar topographic allow for detailed fault analysis where fi eld evaluation is diffi cult. The documentation of Holo- data sets, and analyzed those profi les in Micro- cene motion on the Sawtooth fault demonstrates that ENE-directed extension extends across soft Excel. We profi led the fault scarp in selected central Idaho, and that the fault contributes to seismic hazards. areas of lidar coverage using a laser rangefi nder and refl ector, or via transit leveling. In areas INTRODUCTION and metamorphosed Paleozoic wall rocks and lacking lidar coverage, we extended mapping of Detailed topographic analysis using data roof pendants (Fisher et al., 1992). The adjacent the scarp through detailed examination of stereo from lidar (light detection and ranging) has basin contains sediments of estimated Neogene aerial photographs and other data, coupled with revolutionized mapping of active faults in areas to Quaternary age, overlain by middle and late fi eld investigation in selected areas. of dense vegetative cover, resulting in the iden- Pleistocene glacial landforms. Deglaciation tim- tifi cation of previously unknown, active faults ing near the range front was estimated from 10Be RESULTS (e.g., Johnson et al., 2004; Hunter et al., 2011) exposure dating of moraine boulders (11.3 ka; and enhancing understanding of known faults Sherard, 2006) and from radiocarbon dating Fault Scarp Characteristics (e.g., Harding and Berghoff, 2000). Highly of lake sediment (14 ka; Thackray et al., 2004; Our analysis indicates a previously unmapped detailed topographic data sets and accurate bare- Mijal, 2008). Thus, we use a range of 11.3– topographic lineament along the range front. earth digital elevation models derived through 14 ka for the Pleistocene deglacial landscape This lineament cuts latest Pleistocene–Holo- digital vegetation removal make lidar an ideal disrupted by the Sawtooth fault scarp. Holocene cene landforms (Fig. 1B), and we interpret it tool for locating fault scarps. Here we document alluvial landforms (undated, assumed age 5 ka) as a fault scarp. We identifi ed a continuous previously unknown latest Pleistocene–Holo- locally incise Pleistocene landforms. scarp in several areas on our northern lidar data cene offset on the Sawtooth fault, a major range- The Sawtooth fault has previously been set, spanning 10 km of range-front length. The bounding normal fault in central Idaho (United inferred along the range front based on the scarp is generally a single-strand feature and States), with important implications for regional extreme relief (1300 m) and abrupt, linear lies within 1 km of the topographic range front. tectonic processes. We highlight the utility of topographic change from valley to mountain. It is best developed in latest Pleistocene (post– lidar analysis, not only for identifying young The fault is broadly inferred to have been 14 ka) glacial landforms. On our southern lidar fault scarps, but also for digital evaluation of active during late Quaternary time (Geomatrix data set (5 km of range-front length), the scarp fault characteristics in remote wilderness areas Consultants, Inc., 1989; Breckenridge et al., is discontinuous, and clearly recognized in where terrain and access hinder detailed study. 2003; Crone and Neier, 2003). However, latest only a few locations. In only one location, the We fi nd that lidar analysis can be as effective as Pleistocene–Holocene fault scarps remained observed scarp lineament is broken and exhib- detailed fi eld study in the initial evaluation of unidentifi ed despite decades of surface geo- its a possible left-stepping, en echelon offset. fault characteristics and hazards. logic work along the forested, topographically Stream channels that incise directly across the complex range front (Williams, 1961; Thack- scarp exhibit no clear lateral offset. SETTING AND CONTEXT ray et al., 2004; Sherard, 2006). Between and beyond the areas of lidar cov- Located in the northeastern corner of the erage, the fault scarp is represented on aerial Basin and Range province in central Idaho, LIDAR ACQUISITION AND photographs as lineaments of vegetation, water- the east-dipping Sawtooth fault separates the PROCESSING courses, and topography. These features coincide Sawtooth Mountains from a structural basin This study employed lidar data comple- with the imaged scarp where the lidar data exist, comprising the Sawtooth Valley and Stanley mented by aerial photograph analysis and fi eld and can be mapped at various levels of confi - Basin (Figs. 1A and 1B). The Basin and Range mapping. We utilized two lidar data sets, col- dence for 65 km along the Sawtooth range front. is a 750-km-wide extensional tectonic province lected in 2005 by Airborne 1, Inc. (Fig. 1A). Field surveys at fi ve locations covered by with Miocene–Holocene fault activity. Its north- Data were processed to bare-earth (last return) lidar imagery and at six additional locations eastern corner includes several active faults that digital elevation models (DEMs) using meth- confi rm that the fault scarp exists, continuously have produced Pleistocene to Holocene ruptures, ods described in detail by Streutker and or discontinuously, along at least 55 km of including the A.D. 1983, M 6.9, Borah Peak Glenn (2006). The two data sets cover an area range-front length, from Stanley Lake to Pettit earthquake (Fig. 1C). The Sawtooth Mountains >100 km2 and include fi rst- and last-pulse data Lake, and may extend an additional 10 km south expose Cretaceous granodiorite, Eocene granite, with small point footprints (~30 cm). The bare- (Fig. 1A). At Fishhook Creek (Fig. 1B), the scarp earth DEM processing assumes a semi-open is characterized by a single, 4.1–6.5-m-high *E-mail: [email protected]. canopy, iteratively interpolates the ground step in late Pleistocene valley-bottom glacial

GEOLOGY, June 2013; v. 41; no. 6; p. 639–642; Data Repository item 2013182 | doi:10.1130/G34095.1 | Published online 16 April 2013 ©GEOLOGY 2013 Geological | June Society 2013 | ofwww.gsapubs.org America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. 639

Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/41/6/639/3544297/639.pdf by 19774 on 02 April 2020 topographic profi les across the scarp at 25 loca- A 115º W B tions (8 fi eld checked) in the Redfi sh Lake lidar coverage area (Fig. 1A), using the profi ler tool in ArcGIS 9.2 (ESRI, 2006) on bare-earth lidar

Stanley Lake DEMs (see Table DR1 in the GSA Data Reposi- Stanley Basin tory1). On 16 of those profi les, the scarp is dis- Stanley cernible and readily measured, while on the Fishhook valley remaining 9 profi les, the scarp height is ambigu- ous in complex topography. The 16 topographic Fig. 2 profiles profi les in which the scarp is readily discernible Fig 1b document down-to-the-east vertical offset of 6.3 ± 1.5 m (4.1–8.7 m, n = 12) in Pleistocene land- forms (11.3–14 ka), and 3.0 ± 0.5 m (2.5–3.5 m,

Redfish Lake n = 4) in Holocene alluvial landforms. The scarp heights do not show a statistically signifi - cant trend with distance along the 10 km fault 0 500 m length, and height measurements are elsewhere

Sawtooth Valley too sparse to determine trends over longer scarp lengths. The inferred slip rate, assuming range- Hell Roaring Creek front deglaciation at 14 ka, is 0.5 ± 0.1 mm/yr (60° assumed fault dip) to 0.9 ± 0.2 mm/yr (30°). 44º N To assess the accuracy of topographic pro- 0 5 km fi les derived from the bare-earth DEMs, we compared profi les derived from (1) the bare- Pettit Yellowbelly Lake Lake earth DEM, (2) the raw (vegetated) DEM, and Fault scarp, observed (3) our fi eld-surveyed profi les. On an example

Fault scarp, inferred profi le at Fishhook Creek (Figs. 1B and 2), the raw lidar DEM and the corresponding bare- Lidar coverage earth DEM yield a scarp height estimate within 0.1 m of each other. A corresponding topo- graphic profi le measured with a laser range- C fi nder documents scarp height within 0.2 m of 45º N that derived from the bare-earth lidar profi le. However, our laser rangefi nder profi le uniquely documented a shallow depression (graben?) at the base of the scarp.

n Snake

EasterRiver Plain DISCUSSION 115º W Implications for Lidar-Assisted Fault Figure 1. A: Hillshade image of Sawtooth Mountains range front (Idaho, United States), de- Analyses rived from 10 m digital elevation model. Solid line indicates fault scarp observed from lidar imagery and/or in the fi eld; dashed line indicates fault scarp inferred from aerial photography. Previous studies have shown the merits of B: Bare-earth lidar hillshade image of the Fishhook Creek area. Fault scarp is represented lidar in fault scarp identifi cation and evalu- as a prominent line (arrows) transecting the dominant grain of the glaciated landscape. See ation. However, our study has demonstrated the Data Repository (see footnote 1). C: Map of regional faults with documented Holocene two applications of lidar techniques that are movement. Faults: S—Sawtooth; LR—Lost River; L—Lemhi; B—Beaverhead; R—Red Rock. Box shows approximate location of A. important in the study of faults limited by veg- etation, topography, and access. First, the algo- rithm for removing dense vegetation yields bare-earth DEMs that can produce fault scarp landforms. Nearby, the scarp cuts Holocene The fault scarp is more clearly expressed and profi les very similar to those from fi eld survey alluvial landforms and is also a single step, continuous in the northern 40 km of its mapped (Fig. 2). Second, when lidar data are collected 2.5–3.3 m high (Fig. 2). Southeast of Stanley length. In contrast, we could locate the scarp in at small point spacing (<0.5 m here), the bare- Lake, an area lacking lidar coverage, the scarp only two of six locations examined in the south- earth DEM permits scarp evaluation over many was mapped from aerial photos as a topographic ern 15–25 km. The transition appears to lie in lineament following the trend of a small valley, the Hell Roaring Creek area (Fig. 1A). There, parallel to the range front. There, fi eld observa- the range front has less relief and is somewhat 1GSA Data Repository item 2013182, Table DR1 tions confi rm that the scarp is ~6 m high in gla- more deeply embayed. We infer that a fault seg- (Sawtooth fault scarp measurements and slip rate cal- culations), Table DR2 (comparison of central Idaho cial landforms. At all locations measured in the ment boundary may exist in this area. fault segments with respect to fault segment length, fi eld, the scarp is 4–9 m high in late Pleistocene slip, recurrence interval, slip rates, and timing of landforms. These observations indicate the lidar Detailed Analysis of Lidar-Derived Scarp most recent events), and Figure DR3 (high-resolution imagery (and some of the aerial-photo analysis) Profi les version of Figure 1B), is available online at www provides an accurate record of the scarp location In order to determine scarp offset and estimate .geosociety.org/pubs/ft2013.htm, or on request from [email protected] or Documents Secretary, and surface geometry. slip rates with our most reliable data, we derived GSA, P.O. Box 9140, Boulder, CO 80301, USA.

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Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/41/6/639/3544297/639.pdf by 19774 on 02 April 2020 Stanley Basin lies north of a prominent gravity low (Mabey and Webring, 1983; Webring and Mabey, 1995) that indicates a relatively deep sedimentary basin beneath the Sawtooth Val- ley (Fig. 1A), while a less-distinct and narrower gravity low characterizes the Stanley Basin itself. These observations suggest that cumula- tive slip on the Sawtooth fault has been greatest along its southern trace, while more recent slip has been greatest along its northern trace. Thus, late Cenozoic fault activity may have shifted from south to north, similar to patterns along the three other major faults.

Implications for Seismic Hazards The potential seismic hazard can be estimated from fault parameters. The entire length of the Sawtooth fault, as mapped from lidar and aerial photographs, is 55–65 km. As noted, a segment boundary may lie near Hell Roaring Creek. If the 2–3 m offset of Holocene landforms (e.g., Fig. 2) is characteristic of a single event (similar to the 1983 M 6.9 Borah Peak event [Crone et al., 1987]), then the 4–9 m offset of deglacial Figure 2. Topographic profi les of the 2.5 m scarp of the Sawtooth fault cutting a Holocene landforms is evidence of two to three events alluvial surface at Fishhook Creek, Idaho, United States (Fig. 1B), from raw lidar digital eleva- since 11–14 ka. These relationships suggest a tion model (DEM), bare-earth lidar DEM, and fi eld survey. Note the general consistency of the three profi les. recurrence interval of 3.7–7 k.y., within, or per- haps shorter than, the typical range of recurrence intervals for the regional faults (e.g., Hanks and Schwartz, 1987; Vincent, 1995). Recent analy- kilometers of fault length in dense forest and measurements of 6–8 k.y. between the two most sis of subaqueous landslide deposits in Redfi sh complex geomorphology. recent events on two segments, and 14–20 k.y. Lake indicates a major earthquake disturbance prior to the penultimate event on one segment at ca. 4.1 cal. [calibrated] kyr B.P. and an ear- Implications for Regional Tectonics (Hemphill-Haley et al., 1992, 2000). The Saw- lier disturbance at ca. 7 cal. kyr B.P. (Johnson, The Sawtooth fault accommodates ENE- tooth fault, with a 4–9-m-high scarp cutting sed- 2010), broadly consistent with the recurrence directed crustal extension characteristic of the iments dated at 11–14 ka and evidence for two estimates above. northern Basin and Range province (Table DR2 to three discrete events, is comparable to these A large earthquake on the Sawtooth fault in the Data Repository). Recent slip on other major faults. would have both local and regional effects. The regional faults is demonstrated by Holocene Continuous GPS data indicate ENE-directed town of Stanley (A.D. 2010 year-round popu- fault scarps (Haller, 1988; Breckenridge et extensional strain rate of 7.3 ± 0.4 × 10−9 yr–1 lation of 63) lies within 6 km of the faulted al., 2003; Crone and Neier, 2003), seismicity from the Sawtooth fault to the Montana cra- range front and squarely within the likely epi- (Anders et al., 1989), trench analyses (Hemp- ton (Payne et al., 2008, 2012), equivalent to an central area, and would probably experience hill-Haley et al., 1992; Olig et al., 1995), and extension rate of 2.6 mm/yr across 350 km. If very strong shaking. Large, heavily touristed, historic rupture on the Lost River fault (Crone extension across the eastern half of this tran- moraine-dammed lakes that lie in the hanging et al., 1987). Although the Sawtooth fault was sect were accommodated by the four major wall of the fault might experience lake waves long presumed to form part of this fault set (e.g., faults, each dipping 45°, each fault should have (seiches and/or tsunami). A major Sawtooth Crone and Neier, 2003), this study documents an average slip rate of 0.45 mm/yr. This rate is earthquake could cause moderate shaking in for the fi rst time its postglacial movement. approximately double the slip rates estimated the Wood River Valley (population 22,000, The Sawtooth fault is a signifi cant regional for the active central segments of the three 40 km south) and in the Boise metropolitan structure. Three major faults, the Beaverhead, eastern faults (Haller et al., 1992; Haller and area (population 617,000, 100 km southwest). Lemhi, and Lost River faults, accommodate Wheeler, 1992, 1993), and slightly less than active crustal extension east of the Sawtooth our preliminary slip rate for the Sawtooth fault. CONCLUSIONS AND FURTHER WORK fault (Fig. 1C). Each fault consists of 6–7 seg- Whether the defi cit is accommodated by slip on Clearly, lidar is a powerful tool for recogniz- ments, each ~15–25 km long (Scott et al., 1985; several minor faults or is an artifact of compar- ing and quantifying active faults. Lidar topo- Crone and Haller, 1991; Turko and Knuepfer, ing decadal to millennial rates is unclear. graphic data sets can be used not only for iden- 1991). Eleven centrally located segments typi- The Sawtooth fault scarp pattern appears to tifying scarps obscured by forest or topography, cally show 4–6-m-high scarps cutting sediments refl ect regional patterns. For example, the other but also for preliminary determination of fault dated at 15–30 ka (Haller et al., 1992; Haller and three major faults in eastern Idaho are active offset and estimation of recurrence intervals. Wheeler, 1992, 1993), the result of two to three mainly along their central segments (Anders In the case of the Sawtooth fault, this method discrete slip events documented by trench stud- et al., 1989; Pierce and Morgan, 1992). The has yielded a robust initial data set and provides ies (Vincent, 1995; Hemphill-Haley et al., 1992, postglacial Sawtooth fault scarp appears to be guideposts for further work. 2000). These results suggest recurrence intervals more continuous, with range-front relief great- Recognition of the postglacial Sawtooth fault of ~5–15 k.y., with specifi c recurrence-interval est, adjacent to the Stanley Basin (Fig. 1A). The scarp extends the region of known Holocene

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Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/41/6/639/3544297/639.pdf by 19774 on 02 April 2020 extensional faulting into central Idaho. The Quaternary [M.S. thesis]: Boulder, University and Simpson, D., 1995, Paleoseismic investiga- Sawtooth fault indicates ENE extension similar of Colorado, 141 p., 10 plates. tion of the southern Lost River fault zone, Idaho: Haller, K.M., and Wheeler, R.L., compilers, 1992, Lost Idaho Falls, Idaho, technical report to Lockheed to that infl uencing major faults in east-central River fault: U.S. Geological Survey, Quaternary Idaho Technologies Company, Idaho National Idaho and southwest Montana. Postglacial off- Fault and Fold Database of the United States: Engineering Laboratory, contract C93–134020, sets of 4–9 m and late Cenozoic activity increas- http://earthquakes.usgs.gov/hazards/qfaults. 81 p., 5 plates. ing from south to north place the Sawtooth fault Haller, K.M., and Wheeler, R.L., compilers, 1993, Payne, S.J., McCaffrey, R., and King, R.W., 2008, in a common tectonic pattern of faults north of Lemhi fault: U.S. Geological Survey, Quaternary Strain rates and contemporary deformation in Fault and Fold Database of the United States: the Snake River Plain and surrounding Basin the Snake River Plain. The fault indicates greater http://earthquakes.usgs.gov/hazards/qfaults. and Range from GPS and seismicity: Geology, seismic potential in the region, and should be Haller, K.M., Wheeler, R.L., and Adema, G.W., com- v. 36, p. 647–650. doi:10/1130/G25039A.1. incorporated in regional hazard assessment. pilers, 1992, Beaverhead fault: U.S. Geological Payne, S.J., McCaffrey, R., King, R.W., and Kat- Survey, Quaternary Fault and Fold Database of ternhorn, S.A., 2012, A new interpretation of ACKNOWLEDGMENTS the United States: http://earthquakes.usgs.gov deformation rates in the Snake River Plain and /hazards/qfaults. adjacent Basin and Range regions based on GPS We thank Chris Kemp, Eric Johnson, Joshua Hanks, T.C., and Schwartz, D.P., 1987, Morphologic measurements: Geophysical Journal Interna- Keeley, and Brandon Mijal for assistance with fi eld dating of the pre-1983 fault scarp on the Lost tional, v. 189, p. 101–122, doi:10.1111/j.1365 investigations, and Kemp for assistance with lidar River fault at Doublespring Pass Road, Custer -246X.2012.05370.x. fault scarp analysis. Lidar acquisition and portions County, Idaho: Bulletin of the Seismological Pierce, K.L., and Morgan, L.A., 1992, The track of of the fi eld investigation were funded through the Society of America, v. 77, p. 837–846. the Yellowstone hotspot: Volcanism, faulting NASA Idaho Experimental Program to Stimulate Harding, D.J., and Berghoff, G.S., 2000, Fault scarp and uplift, in Link, P.K., Kuntz, M.A., and Competitive Research Grant FPK302-02. We thank detection beneath dense vegetation cover— Platt, L.B., eds., Regional Geology of Eastern three anonymous reviewers, whose comments im- Airborne laser mapping of the Seattle fault Idaho and Western Wyoming: Geological Soci- proved the manuscript signifi cantly. zone, Bainbridge Island, Washington State, in ety of America Memoir 179, p. 1–53. Proceedings of the American Society of Photo- Scott, W.E., Pierce, K.L., and Hait, M.H., Jr., 1985, REFERENCES CITED grammetry and Remote Sensing Annual Confer- Quaternary tectonic setting of the 1983 Borah Anders, M.H., Geissman, J.W., Piety, L.A., and Sulli- ence, Washington, D.C., May 2000, 9 p. Peak earthquake, central Idaho: Bulletin of van, J.T., 1989, Parabolic distribution of circum- Hemphill-Haley, M.A., Knuepfer, P.L.K., Forman, the Seismological Society of America, v. 75, eastern Snake River Plain seismicity and latest S.L., and Smith, R.P., 1992, Paleoseismic in- p. 1053–1066. Quaternary faulting: Migratory pattern and as- vestigations of the southern Lemhi fault, Idaho: Sherard, C., 2006, Regional correlations of late sociation with the Yellowstone hotspot: Journal technical report to U.S. Department of Energy, Pleistocene climatic changes based on cos- of Geophysical Research, v. 94, p. 1589–1621, contract DE-AC07–761D01570, 32 p. mogenic nuclide exposure dating of moraines doi:10.1029/JB094iB02p01589. Hemphill-Haley, M.A., Sawyer, T.L., Knuepfer, in Idaho [M.S. thesis]: Bellingham, Western Breckenridge, R.M., Lewis, R.S., Adema, G.W., P.L.K., Forman, S.L., and Wong, I.G., 2000, Washington University, 87 p. and Weisz, D.W., 2003, Miocene and younger Timing of faulting events from thermolumines- Streutker, D., and Glenn, N., 2006, LiDAR measure- faults in Idaho: Idaho Geological Survey Map cence dating of scarp-related deposits, Lemhi ment of sagebrush steppe vegetation heights: 8, scale 1:1,000,000, 1 sheet. fault, southeastern Idaho, in Stratton-Noller, Remote Sensing of Environment, v. 102, Crone, A.J., and Haller, K.M., 1991, Segmentation J., Sowers, J.M., and Lettis, W.R., eds., Qua- p. 135–145, doi:10.1016/j.rse.2006.02.011. and the coseismic behavior of Basin and Range ternary geochronology—Methods and applica- Thackray, G.D., Lundeen, K.A., and Borgert, J.A., normal faults: Examples from east-central Idaho tions: Washington, D.C., American Geophysi- 2004, Latest Pleistocene alpine glacier advances and southwestern Montana, in Hancock, P.L., cal Union Reference Shelf, v. 4, p. 541–548. in the Sawtooth Mountains, Idaho, USA—Re- Yeats, R.S., and Sanderson, D.J., eds., Charac- Hunter, L.E., Howle, J.F., Rose, R.S., and Bawden, fl ections of mid-latitude moisture transport at teristics of active faults: Journal of Structural G.W., 2011, Lidar assisted identifi cation of an the close of the last glaciation: Geology, v. 32, Geology, v. 13, p. 151–164. active fault near Truckee, California: Bulletin of p. 225–228, doi:10.1130/G20174.1. Crone, A.J., and Neier, R.S., compilers, 2003, Fault the Seismological Society of America, v. 101, Turko, J.M., and Knuepfer, P.L.K., 1991, Late Quater- number 640, Sawtooth fault: U.S. Geological p. 1162–1181, doi:10.1785/0120090261. nary fault segmentation from analysis of scarp Survey, Quaternary Fault and Fold Database of Johnson, E.M., 2010, Lacustrine evidence of seismic morphology: Geology, v. 19, p. 718–721, doi: the United States: http://earthquakes.usgs.gov events on the Sawtooth Fault in the Redfi sh Lake 10.1130/0091-7613(1991)019<0718:LQFSFA> /regional/qfaults (June 2012). drainage, Sawtooth Mountains, central Idaho 2.3.CO;2. Crone, A.J., Machette, M.N., Bonilla, M.G., Lien- [M.S. thesis]: Pocatello, Idaho State University, Vincent, K.R., 1995, Implications for models of fault kaemper, J.J., Pierce, K.L., Scott, W.E., and 116 p. behavior from earthquake surface-displace- Bucknam, R.C., 1987, Surface faulting ac- Johnson, S.Y., Nelson, A.R., Personius, S.F., Wells, ment along adjacent segments of the Lost River companying the Borah Peak earthquake and R.E., Kelsey, H.M., Sherrod, B.L., Okumura, fault, Idaho [Ph.D. thesis]: Tucson, University segmentation of the Lost River fault, central K., Koehler, R., III, Witter, R.C., Bradley, L.-A., of Arizona, 152 p. Idaho: Bulletin of the Seismological Society of and Harding, D.J., 2004, Evidence for late Ho- Webring, M.W., and Mabey, D.R., 1995, Geophysical America, v. 77, p. 739–770. locene earthquakes on the Utsalady Point fault, anomalies, in Fisher, F.S., and Johnson, K.M., ESRI, 2006, ArcGIS 9.2 software: Redlands, Cali- northern Puget Lowland, Washington: Bulletin eds., Geology and mineral resource assessment fornia, ESRI Corporation. of the Seismological Society of America, v. 94, of the Challis 1° × 2° quadrangle, Idaho: U.S. Fisher, F.S., McIntyre, D.H., and Johnson, K.M., p. 2299–2316, doi:10.1785/0120040050. Geological Survey Professional Paper 1525, 1992, Geologic map of the Challis 1° × 2° quad- Mabey, D.R., and Webring, M.W., 1983, Regional p. 53–62. rangle, Idaho: U.S. Geological Survey Miscel- geophysical studies in the Challis quadrangle, Williams, P.L., 1961, Glacial geology of Stanley Ba- laneous Investigations Series Map I-1819, scale in McIntyre, E.H., ed., Symposium on the Geol- sin: Idaho Bureau of Mines and Geology Pam- 1:250,000, 1 sheet. ogy and Mineral Deposits of the Challis 1° × 2° phlet 123, 29 p. Geomatrix Consultants, Inc., 1989, Final report seis- quadrangle, Idaho: U.S. Geological Survey Bul- motectonic evaluation for Little Wood River letin 1658, p. 69–79. Dam site: Technical report to U.S. Department Mijal, B., 2008, Holocene and latest Pleistocene of Interior: Denver, Colorado, Bureau of Rec- glaciations in the Sawtooth Mountains, cen- Manuscript received 3 October 2012 lamation, 104 p., 2 plates. tral Idaho [M.S. thesis]: Bellingham, Western Revised manuscript received 8 January 2013 Haller, K.M., 1988. Segmentation of the Lemhi and Washington University, 90 p. Manuscript accepted 9 January 2013 Beaverhead faults, east-central Idaho, and Red Olig, S.S., Gorton, A.E., Bott, J.D., Wong, I.G., Rock fault, southwest Montana, during the late Knuepfer, P.L.K., Forman, S.L., Smith, R.P., Printed in USA

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