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Complete Report for Saddle Mountains structures, Saddle Mountains fault (Class A) No. 562a

Brief Report ||Partial Report

citation for this record: Lidke, D.J., compiler, 2002, Fault number 562a, Saddle Mountains structures, Saddle Mountains fault, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 04/19/2014 02:34 PM.

Synopsis General: The east-trending Saddle Mountains structures include the Saddle Mountains fault and some apparently related normal faults that show evidence of Quaternary offset (Reidel, 1984 #5545; Reidel and others, 1994 #3539; West and others, 1996 #3514; West, 1997 #5548). The Saddle Mountains anticline and related folds and some faults of the Saddle and Boylston Mountains, however, are only known to deform Miocene and Pliocene rocks. Quaternary age growth or tightening of the Saddle Mountains folds and other folds in the Yakima fold belt, has been suggested and inferred from several local and regional geologic relations in the Yakima fold belt (Campbell and Bentley, 1981 #3513; Reidel, 1984 #5545; Reidel and others, 1994 #3539). For the Saddle Mountains, Reidel (1984 #5545) inferred Quaternary growth of the folds based on Miocene and post-Miocene uplift of Miocene volcanic rocks in the core of the Saddle Mountains relative to Miocene volcanic rocks in the adjacent synclinal valleys. West and others (1996 #3514) and West (1997 #5548) reported on Quaternary normal faults and a graben, which are present in the Smyrna Bench area of the Saddle Mountains, and they interpreted these normal faults as hanging-wall tensional features related to Quaternary movement along the underlying Saddle Mountains fault. They noted that the Saddle Mountains anticline probably cannot accommodate much additional strain by folding and that additional strain would likely instead induce fault slip. No unequivocal evidence for Quaternary growth or tightening of major folds in the Saddle Mountains has been documented or described. Consequently, the Saddle Mountains anticline and related folds, as well as some of the faults in the Saddle and Boylston Mountains, are classified herein as class B structures until further studies are conducted.

Sections: This fault has 2 sections.
Name comments General:


Section:
The Saddle Mountains fault was mapped as an unnamed vertical fault by Grolier and Bingham (1971 #5542) and is referred to as the Saddle Mountains fault by Grolier and Bingham (1978 #5543), Reidel (1984 #5545), Reidel (1988 #5546), Reidel and Fecht (1994 #5565), and Reidel and others (1994 #3539). Detailed studies, which are discussed in West and others (1996 #3514) and West (1997 #5548) identified a graben and normal faults that displace Quaternary deposits in the Symrna Bench area of the Saddle Mountains. These normal faults offset late Pleistocene-Holocene sediments, are interpreted as tensional features related to movement along the Saddle Mountains fault (West and others, 1996 #3514; West, 1997 #5548), and are discussed herein with the Saddle Mountains fault. The Saddle Mountains fault is mapped as a thrust fault that coincides with north flank of the Saddle Mountains and at a minimum the fault extends from the Columbia River eastward to directly west of Eagle Lakes (Reidel and Fecht, 1994 #5565; Schuster and others, 1997 #3760). An apparent continuation of the Saddle Mountains fault is mapped west of the Columbia River in Miocene volcanic rocks along the northern flank of the Saddle and Boylston Mountains (Reidel, 1984 #5545; Schuster and others, 1997 #3760). No evidence for Quaternary deformation related to faults and folds of the Saddle and Boylston Mountains has been documented west of the Columbia River.
County(s) and State(s) ADAMS COUNTY, WASHINGTON
FRANKLIN COUNTY, WASHINGTON
KITTITAS COUNTY, WASHINGTON
GRANT COUNTY, WASHINGTON
Physiographic province(s) COLUMBIA PLATEAU
Reliability of location Good
Compiled at 1:250,000 scale.

Comments: Location of Saddle Mountain fault is mostly from the 1:250,000-scale geologic map of Schuster and others (1997 #3760). The approximate outline of the graben in the Symrna Bench area of the Saddle Mountains and the mostly inferred trace of the Saddle Mountains fault in the Smyrna Bench area are from West (1997 #5548) and were reduced and compiled at 1:250,000 scale. The 1:250,000-scale geologic map by Schuster and others (1997 #3760) is compiled from the 1:100,000-scale geologic map by Reidel and Fecht (1994 #5565).

Geologic setting The Saddle and Boylston Mountains lie in the northeastern part of the Yakima fold belt, a structural-tectonic sub province of the western Columbia Plateaus Province (Reidel and others, 1989 #5553; 1994 #3539). The Yakima fold belt consists of a series of generally east-trending narrow asymmetrical anticlinal ridges and broad synclinal valleys formed by folding of Miocene Columbia River basalt flows and sediments. In most parts of the belt the folds have a north vergence with the steep limb typically faulted by imbricate thrust faults. According to Reidel and others (1989 #5553) these frontal faults are typically associated with the areas of greatest structural relief. In the few places where erosion exposes the frontal faults deeper in the cores of the anticlinal ridges the faults are seen to become steeper with depth (as steep as 45? to 70?). Along their lengths the anticlines are commonly broken into segments ranging between 5 and 35 km long with boundaries defined by abrupt changes in fold geometry. Anticlinal ridges of the Yakima fold belt began to grow in Miocene time (about 16-17 Ma), concurrent with eruptions of Columbia River basalt flows, and continued during Pliocene time and may have continued to the present (Reidel and others, 1989 #5553; 1994 #3539).

The south-dipping Saddle Mountains fault is a thrust fault that cuts the north limb of the north-vergent Saddle Mountains anticline, one of the many anticlinal ridges that comprise the Yakima fold belt in south-central Washington. The Saddle Mountain anticline and related folds deform rocks of the Columbia River Basalt Group (Miocene) and overlying sedimentary rock (Pliocene). Quaternary deformation is generally associated with the most tightly folded and structurally complex interval of the anticline (West, 1997 #5548). Quaternary faulting also includes development of grabens and beheading of modern streams in the hanging wall south of the Saddle Mountains thrust fault. This is analogous to surface rupture accompanying the Oct. 10, 1980, El Asnam, Algeria, M 7.3 earthquake (Philip and Meghraoui, 1983 #5544; Meghraoui and others, 1988 #803; Avouac and others, 1992 #5540). Contemporary seismicity in and near the Saddle Mountains also suggests late Quaternary tectonism (Ludwin and Qamar, 1995 #1350). Campbell and Bentley (1981 #3513) and Mann and Meyer (1993 #3535) reported and suggested late Quaternary deformation on other structures in the Yakima foldbelt.

Length (km) This section is 60 km of a total fault length of 104 km.
Average strike N71°W (for section) versus N71°W (for whole fault)
Sense of movement Thrust

Comments: The Saddle Mountains fault is shown as a mostly buried thrust fault on geologic maps by Reidel (1988 #5546), Reidel and Fecht (1994 #5565), and Schuster and others (1997 #3760). From trench exposures West (1994 #5547; 1997 #5548) confirmed the fault as a thrust. Detailed studies by West (1994 #5547; 1997 #5548) also identified a graben and numerous normal faults in the region directly south of the Saddle Mountains fault in the Smyrna Bench area. The graben and normal faults deform Quaternary sediments and these features are interpreted as tensional structures related to late Pleistocene to Holocene movement along the Saddle Mountains fault (West and others, 1996 #3514; West, 1997 #5548).

Dip 10° - 60°

Comments: The Saddle Mountains fault is poorly exposed. Detailed studies of trenches showed the basal shear zone of the Saddle Mountains fault dipping 9?-18? S, and showed smaller subsidiary thrusts dipping 30?-40? S (West and others, 1996 #3514; West, 1997 #5548). For an idealized model of the Saddle Mountains fault, Reidel (1984 #5545), citing Grolier and Bingham (1978 #5543), assumed a dip of about 45? at depth based on the dip of the Frenchman Hills fault exposed 20 km to the north along the Columbia River. Reidel (1984 #5545) notes that near the surface the fault is imbricate with the dip controlled by the dip of basalt flows north of the uplift. Reidel and others (1989 #5553) reported that in the few places where erosion exposes the frontal faults deeper in the cores of the anticlinal ridges, the faults are seen to become steeper with depth (as steep as 45? to 70?). Geomatrix Consultants Inc. (1996 #4676) used fault dips of 30?, 45?, and 60? in their calculations of slip rates for the Saddle Mountains fault. West and others (1996 #3514) modeled the fault using dips of 20?-40?. West and others (1996 #3514) and West (1997 #5548) show moderate to steep dips for normal faults exposed in trenches south of the Saddle Mountains fault in the Smyrna Bench area.

Paleoseismology studies West and Shaffer (1988 #5549) and West (1994 #5547; 1997 #5548) collectively excavated and mapped four trenches (Sites 575-1 to 574-4) across the Saddle Mountains fault, across apparent late Quaternary faults on the northern flank of a 13-km-long graben, and across an ~5-m-high scarp north of the graben. For the westernmost trench, which crossed the Saddle Mountains fault, West (1997 #5548) reported that relations of shear zones, colluvial wedges, and soil development suggest a late Pleistocene to Holocene event with about 1.3 m of surface offset as well as two or more older Pleistocene events. West and others (1996 #3514) and West (1997 #5548) concluded, from a trench across the northern fault of the graben, that the graben is tectonic in origin and probably related to movement on the underlying Saddle Mountains fault. Dating of deformed Quaternary sediments and paleosols in this trench across the graben also indicated that graben development began about 100 ka and continued into the Holocene (West and others, 1996 #3514; West, 1997 #5548). The two eastern trenches cross a 5-m-high scarp but these trenches did not reveal the Saddle Mountains fault as was initially expected. These trenches instead exposed medial and distal parts of stacked colluvial wedges that were interpreted by West (1997 #5548) as deposits that formed from loess "avalanching" triggered by surface fault ruptures upslope.

Trench 562A-1 was excavated in 1987 by West and Shaffer (1988 #5549) across a 5-m-high scarp and is also shown and discussed in West (fig. 3, 1997 #5548).

Trench 562A-2 was excavated in 1994 by West (1994 #5547) near Trench 562A-1 across the same 5-m-high scarp and is also shown and discussed in West (fig. 3, 1997 #5548).

Trench 562A-3 was excavated in 1994 by West (1994 #5547) across the northern fault of the Syrna Bench graben and is also shown and discussed in West (fig. 3, 1997 #5548).

Trench 562A-4 was excavated in 1997 by West (fig. 3, 1997 #5548) across the trace of the Saddle Mountains fault.

Geomorphic expression The Saddle Mountains fault is poorly exposed and is mapped as a buried fault along most of its trace. A thick mantle of highly mobile Holocene loess and colluvium, as well as talus and landslide deposits, obscure and bury most of the northern flank of the Saddle Mountains (Grolier and Bingham, 1971 #5542; Reidel, 1988 #5546; Reidel and Fecht, 1994 #5565; Schuster and others, 1997 #3760). Primary geomorphic evidence of Quaternary faulting along the trace of the Saddle Mountains fault is sparse. West and Shaffer (1988 #5549), Geomatrix (1990 #5550), and West (1997 #5548) reported the presence of some lineaments along and near the trace of the fault in the area north of Smyrna Bench and east of the Bench. They also reported that an erosional origin was possible for some or all of these lineaments. West (1997 #5548) identified a graben immediately inboard (south) of the buried thrust trace(s) in the Smyrna Bench area and noted that the primary geomorphic expression of the graben was disruption of streams by offsets along normal faults that beheaded some streams and created local depressions (sag ponds). A 5-m-high scarp north of the graben, originally interpreted to be the thrust trace, exposed in trenches what is now believed to be the medial and distal parts of colluvial wedges that formed in response to faulting and surface rupture upslope, to the south (West, 1997 #5548). North of Smyrna Bench and the Smyrna Bench graben, the location of the Saddle Mountains fault may be marked by a topographic bulge (West, 1997 #5548).

Age of faulted surficial deposits The most detailed information concerning deformed Quaternary deposits is from trench studies across a graben that is located directly south of the Saddle Mountains fault in the Smyrna Bench area of the Saddle Mountains (West and others, 1996 #3514; West, 1997 #5548). The graben and associated normal faults are interpreted by West and others (1996 #3514) and West (1997 #5548) to be related to late Pleistocene to Holocene movement along the underlying Saddle Mountains fault. West and others (1997 #5548) identified scarp-derived colluvium in the graben that contains the 6850 14C yr old Mazama climactic tephra (Crandell and others, 1981 #5541). They also identified a faulted 20-40 ka paleosol in the graben that contains the Mt. St. Helens, set M tephra (>18,560?180, and <20350?350 14C yr) as described by (Crandell and others, 1981 #5541; Busacca, 1991 #3598).
Historic earthquake
Most recent prehistoric deformation Late Quaternary (<130 ka)

Comments: West (1997 #5548) infered that the latest event probably occurred about 6850 14C yrs based on the inclusion of Mazama tephra (Crandell and others, 1981 #5541) in scarp-derived, colluvial-wedge deposits in the graben south of the Saddle Mountains fault in the Smyrna Bench area. Based on relations exposed in a trench across the Saddle Mountains fault in Smyrna Bench area, West (1997 #5548) concluded that relations of shear zones, colluvial wedges, and soil development suggest a late Pleistocene to Holocene age for the most recent event. Because relations of the Smyrna Bench graben relative to the Saddle Mountains fault are not tightly constrained, a late Quaternary (<130 ka) age for the most recent event is assigned to the part of the fault near Smyrna Bench. A more speculative Quaternary age is assigned to the remaining parts of the fault that are locally associated with lineaments suggestive of Quaternary fault activity (Geomatrix Consultants Inc., 1990 #5550).

Recurrence interval

Comments: Piety and others (1990 #3733) used uplift rates calculated from 13.5 Ma volcanic rocks to estimate recurrence intervals of 490-24,500 years based on displacement per events of 0.02-1.0 m. Based on relations in a trench that crossed the Saddle Mountains fault, West (1997 #5548) reported that relations of shear zones, colluvial wedges, and soil development suggest a late Pleistocene to Holocene event with about 1.3 m of surface offset as well as two or more Pleistocene events. A minimum of 6.5 m of displacement of a 20-40 ka paleosol along the fault zone bounding the north flank of the Smyrna Bench graben and poorly-developed colluvial wedge stratigraphy, mainly in loess, may indicate multiple events in the last 20-40 ka (West and others, 1996 #3514; West, 1997 #5548). These relations may indicate a recurrence interval that is measured in thousands to tens-of-thousands of years.
Slip-rate category Between 0.2 and 1.0 mm/yr

Comments: Based mostly on uplift of Miocene volcanic rocks, uplift and long-term slip rates have been calculated for the Saddle Mountains anticline or uplift (Reidel, 1984 #5545; Piety and others, 1990 #3733; Geomatrix Consultants Inc., 1996 #4676). Based on normal fault offsets of Quaternary units in a graben, Pleistocene-Holocene slip rates have been calculated for the Smyrn Bench area of the Saddle Mountains and Saddle Mountains fault (West and others, 1996 #3514; West, 1997 #5548). Reidel (1984 #5545) compared relative amounts of uplift of volcanic units in the core of the Saddle Mountains and determined that post-Miocene uplift of the Saddle Mountains was relatively constant and about .04 mm/yr. Piety and others (1990 #3733) report 550 m of uplift of 13.5 Ma volcanic rocks, which yields an uplift rate of 0.04 mm/yr. Geomatrix Consultants Inc. (1996 #4676) used various uplift amounts and ages for Miocence volcanic rocks and used estimated fault dips of 30?, 45?, and 60? to estimate long-term slip rates of 0.007-0.175 mm/yr for an inferred principle fault underlying the Saddle Mountains. Based mostly on detailed studies of faulted units and fault relations along faults of the Smyrna Bench graben, West and others (1996 #3514) and West (1997 #5548) concluded that the graben is tectonic and related to movement along the underlying Saddle Mountains fault. West and others (1996 #3514) and West (1997 #5548) also concluded, based largely on similar relations documented for the El Asnam fold and thrust Belt (Philip and Meghraoui, 1983 #5544; Meghraoui and others, 1988 #803; Avouac and others, 1992 #5540), that vertical and horizontal components of slip in the graben should approximate (less than or equal to) vertical and horizontal components of slip along the primary, causative thrust fault. For normal faults in the graben, West and others (1996 #3514) and West (1997 #5548) calculated a minimum, normal-fault slip rate of 0.16 to 0.33 mm/yr, based on displacement of at least 6.5 m of a 20-40 ka paleosol (Busacca, 1991 #3598). According to West and others (1996 #3514) and West (1997 #5548), resolution of at least 6.5 m of vertical displacement on a 30? dipping thrust fault yields a minimum slip of 13 m in the fault plane in 20-40 ka and minimum thrust slip rates of 0.33 to 0.65 mm/yr. Based on these estimates, the Smyrna Bench area of the Saddle Mountains fault is assigned a slip rate of 0.2-1.0 mm/yr and the remaining parts of the fault are assigned slip rates of <0.2 mm/yr.
Date and Compiler(s) 2002
David J. Lidke, U.S. Geological Survey
References #5540 Avouac, J.P., Meyer, B., and Tapponnier, P., 1992, On the growth of normal faults and the existence of flats and ramps along the El Asnam active fold and thrust system: Tectonics, v. 11, p. 1-11.

#3598 Busacca, A.J., 1991, Loess deposits and soils of the Palouse and vicinity, in Morrison, R.B., ed., Quaternary nonglacial geology; conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. K-2, p. 216-228.

#3513 Campbell, N.P., and Bentley, R.D., 1981, Late Quaternary deformation of the Toppenish Ridge uplift in south-central Washington: Geology, v. 9, p. 519-524.

#5541 Crandell, D.R., Mullineaux, D.R., Rubin, M., Spiker, E., and Kelley, M.L., 1981, Radiocarbon dates from volcanic deposits at Mount St. Helens, Washington: U.S. Geological Survey Open-File Report 81-0844, 16 p.

#5550 Geomatrix Consultants, Inc., 1990, Seismotectonic evaluation of the Walla Walla section of the Columbia Plateau geomorphic province for Grand Coulee, North, Dry Falls, Pinto, and O'Sullivan Dams; Soda Lake, north Scooteney, and south Scooteney dikes: Technical report to U.S. Department of the Interior, Bureau of Reclamation, Denver, Colorado, under Contract 6-CS-81-07310, April 1990, 129 p.

#4676 Geomatrix Consultants, Inc., 1996, Probabilistic seismic hazard analysis DOE Hanford site, Washington: Technical report to Westinghouse Hanford Company, Richland, Washington, under Contract WHC-SD-W236A-TI-002, Rev.1, February, 1996, 366 p.

#5542 Grolier, M.J., and Bingham, J.W., 1971, Geologic map and sections of parts of Grant, Adams and Franklin Counties, Washington: U.S. Geological Survey Geologic Investigations Map I-589, 1 sheet, scale 1:62,500.

#5543 Grolier, M.J., and Bingham, J.W., 1978, Geology of parts of Grant, Adams, and Franklin Counties, east-central Washington: Washington Division of Geology and Earth Resources Bulletin 71, 91 p.

#1350 Ludwin, R.S., and Qamar, A.I., 1995, Historic seismicity catalog and macroseismic accounts for Cascadia, 1793-1929: Technical report to U.S. Geological Survey, under Contract 1434-93-G-2323, September 19,1995, 72 p.

#3535 Mann, G.M., and Meyer, C.E., 1993, Late Cenozoic structure and correlations to seismicity along the Olympic-Wallowa Lineament, northwest United States: Geological Society of America Bulletin, v. 105, p. 853-871.

#803 Meghraoui, M., Philip, H., Albarede, F., and Cisternas, A., 1988, Trench investigations through the trace of the 1980 El Asnam thrust fault--Evidence for paleoseismicity: Bulletin of the Seismological Society of America, p. 979-999.

#5544 Philip, H., and Meghraoui, M., 1983, Structural analysis and interpretation of the surface deformations of the El Asnam earthquake of October 10, 1980: Tectonics, v. 2, p. 17-49.

#3733 Piety, L.A., LaForge, R.C., and Foley, L.L., 1990, Seismic sources and maximum credible earthquakes for Cold Springs and McKay Dams, Umatilla Project, north-central Oregon: U.S. Bureau of Reclamation Seismotectonic Report 90-1, 62 p., 1 pl.

#5545 Reidel, S.P., 1984, The Saddle Mountains--The evolution of an anticline in the Yakima fold belt: American Journal of Science, v. 284, p. 942-978.

#5546 Reidel, S.P., 1988, Geologic map of the Saddle Mountains, south-central Washington: Washington Division of Geology and Earth Resources Geologic Map GM-38, 28 p., 5 pls., scale 1:48,000.

#5565 Reidel, S.P., and Fecht, K.R., 1994, Geologic map of the Priest Rapids 1:100,000 quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 94-13, 22 p. pamphlet, 1 sheet, scale 1:100,000.

#3539 Reidel, S.P., Campbell, N.P., Fecht, K.R., and Lindsey, K.A., 1994, Late Cenozoic structure and stratigraphy of south-central Washington, in Lasmanis, R., and Cheney, E.S., eds., Regional geology of Washington State: Washington Division of Geology and Earth Resources, p. 159-180.

#5553 Reidel, S.P., Fecht, K.R., Hagood, M.C., and Tolan, T.L., 1989, The geologic evolution of the central Columbia Plateau, in Reidel, S.P., and Hooper, P.R., eds., Volcanism and tectonism in the Columbia River flood-basalt province: Geological Society of America Special Paper 239, p. 247-264.

#3760 Schuster, E.J., Gulick, C.W., Reidel, S.P., Fecht, K.R., and Zurenko, S., 1997, Geologic map of Washington-southeast quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-45, 20 p. pamphlet, 2 sheets, scale 1:250,000.

#5547 West, M.W., 1994, A "pilot" study of Quaternary surface deformation, Saddle Mountains anticline, northern Pasco Basin, Washington: Technical report to U.S. Geological Survey, Reston, Virginia, under Contract 1434-94-G-2392, 11 p.

#5548 West, M.W., 1997, A continuation of a "pilot" study of Quaternary surface deformation, Saddle Mountains anticline, northern Pasco Basin, Washington: Technical report to U.S. Geological Survey, Reston, Virginia, under Contract 1434-HQ-97-GR-02999, 33 p.

#3514 West, M.W., Ashland, F.X., Busacca, A.J., Berger, G.W., and Shaffer, M.E., 1996, Late Quaternary deformation, Saddle Mountains anticline, south-central Washington: Geology, v. 24, no. 12, p. 1123-1126.