Lab 2 Part 3
Geology 3265
Name ___________________
The internet provides a rich source of information on your field area.
Here are some online resources pertinent to Smyrna, WA geomorphology. Start here
1. Satellite views Google Maps, Mapquest http://www.mapquest.com/maps?city=Smyrna&state=WA
2. An early study of surface geology, found by google search Saddle Mountains geology Smyrna WA
http://www.dnr.wa.gov/Publications/ger_ofr79-3_columbia_basin_sediments_12k_pt2.pdf
Tr is Tertiary Ringold Formation, NOT Triassic
http://www.dnr.wa.gov/Publications/ger_ofr79-3_columbia_basin_sediments_12k_pt1.pdf
Saddle Mountains Basalt p 16
3. Google Earth searches for Saddle Moountains and Smyrna Bench, WA
Smyrna Bench and Saddle Mountains.kmz
4. Google search for Saddle Mountains Geology
http://academic.research.microsoft.com/Publication/60302968
Geology of the Saddle Mountains between Sentinel Gap and 119°30' longitude,Reidel
Members and flows of the Grande Ronde, Wanapum, and Saddle Mountains basalts of the Columbia
River Basalt Group were mapped in the Saddle Mountains between Sentinel Gap and the eastern edge
of Smyrna Bench. The Grande Ronde Basalt consists of the Schwana (low-MgO) and Sentinel Bluffs (highMgO) members (informal names). The Wanapum Basalt consists of the aphyric and phyric units of the
Frenchman Springs Member, the Roza-Like Member, and the Priest Rapids Member. The Saddle
Mountains Basalt consists of the Wahluke, Huntzinger, Pomona, Mattawa, and Elephant Mountain
basalts. The Wanapum and Saddle Mountains basalts are unevenly distributed across the Saddle
Mountains. The Wanapum Basalt thins from south to north and across a northwest-southeast-trending
axis at the west end of Smyrna Bench. The Priest Rapids, Roza-Like, and aphyric Frenchman Springs units
are locally missing across this zone. The Saddle Mountains basalt has a more irregular distribution and,
within an area between Sentinel Gap and Smyrna Bench, is devoid of the basalt. The Wahluke,
Huntzinger, and Mattawa flows are locally present, but the Pomona is restricted to the southern flank
west of Smyrna Bench, and the Elephant Mountain Basalt only occurs on the flanks and in three
structurally controlled basins on the northwest side. The structure of the Saddle Mountains is
dominated by an east-west trend and, to a lesser degree, controlled by a northwest-southeast and
northeast-southwest trend. The geomorphological expression of the Saddle Mountains results from the
east-west fold set and the Saddle Mountains fault along the north side. The oldest structures follow the
northwest-southeast trend. The distribution of the flows, combined with the structural features,
indicates a complex geologic history for the Saddle Mountains.
Published 1978
5. Kean Libraary Databases, GeoRef
a. New evidence for the nature of the Saddle Mountains fault zone
Tincher, Christopher R; Reidel, Stephen P. Abstracts with Programs - Geological Society of America 41. 7
(October 2009): 226.
Abstract
The western portion of the Columbia River Flood-Basalt Province in Washington northeast Oregon is
characterized by the Yakima fold belt. The fold belt consists of a series of generally west trending
anticlines that are narrow (approx 5 km) and over 100 km long. The anticlines have a frontal fault zone
that, in surface exposures, can dip from 30 degrees to as much as 75 degrees. Resolving the nature of
the fault at depth is difficult due to the inability of most geophysical techniques to have the necessary
resolution. XRF chemical analyses of basalt were used in the 1980s to develop a regional stratigraphy,
which then could be used to look for stratigraphic repeats in boreholes drilled into these folds. The
younger flows are compositionally diverse and could be easily recognized by drill cuttings, but the
Grande Ronde Basalt (GRB), however, proved to be more difficult because of the slight but significant
variations in compositions. In the 1990's, new technology provided high precision XRF analyses making
the GRB easier to recognize and providing a more-powerful tool for fault repeat recognition. In 2006,
EnCana drilled an exploratory hydrocarbon borehole about 5 miles from the Shell-ARCO BN 1-9 that was
drilled in the Saddle Mountains Anticline. The EnCana borehole was drilled south of the Saddle
Mountains providing an unfaulted stratigraphic reference. An earlier study using older XRF basalt
compositions suggested the Saddle Mountains fault did not penetrate the borehole constraining the dip
angle to greater than 65 degrees. Comparing the new EnCana XRF borehole stratigraphy to the BN 1-9
reanalyzed basalt, we were able to resolve a 600 m repeat in the BN 1-9 GRB stratigraphy. This analysis
suggests that the Saddle Mountains fault zone is dipping approximately 30 degrees to the south. This is
the first conclusive data defining the structural dip of a frontal fault zone in a Yakima fold.
b. Revised stratigraphy for several Saddle Mountains and Wanapum Basalt units, Columbia River Basalt
Group. Kauffman, John D; Garwood, Dean L, Abstracts with Programs - Geological Society of America 41.
7 (October 2009): 298.
Recent mapping in the Clearwater embayment in Idaho has clarified ambiguous stratigraphic
relationships of several Columbia River Basalt Group units, and in one instance has shown a unit
previously identified as CRBG to be Oligocene. Clarification of the stratigraphy allows us to better
understand the role these small volume flows play in the eastern Columbia Plateau. In Saddle Mountains
Basalt, the basalt of Craigmont overlies the basalt of Swamp Creek, which overlies the basalt of Weippe;
the basalt of Grangeville has been documented to underlie the basalt of Weippe and overlie the Asotin
Member. Stratigraphic position of the basalt of Feary Creek remains unresolved, although its close
association with other Saddle Mountains Basalt units, composition similar to the Craigmont and Swamp
Creek units, and an age determination of about 11.5-12 Ma strongly suggest it is Saddle Mountains in
age. Basalt of Mica Flat, a previously unidentified unit, overlies a thin sediment interbed above the Priest
Rapids Member south of Coeur d'Alene. We now include it in Saddle Mountains Basalt, but its position
within that formation is uncertain. The basalt of Icicle Flat, previously included in the Saddle Mountains
Basalt, now has been placed in the Wanapum Basalt, and is believed to be equivalent to the basalt of
Dodge, Eckler Mountain Member, on the basis of paleomagnetic directions, composition, and its
stratigraphic position between the Priest Rapids Member and R (sub 2) Grande Ronde Basalt. The extent
of most of these units has also been refined and in some instances expanded. Basalt with Asotin
Member chemistry has been found filling a narrow erosional channel in R (sub 2) Grande Ronde Basalt
on Craig Mountain, the plateau south of the Waha escarpment and east of the Limekiln Fault. The basalt
of Potlatch, Onaway Member, previously included in either Wanapum Basalt or Saddle Mountains
Basalt, has been shown by dating to be Oligocene.
c. Late Quaternary deformation, Saddle Mountains Anticline, south-central Washington. West, M W;
Ashland, F X; Busacca, A J; Berger, G W; Shaffer, M E. Geology (Boulder)24. 12 (December 1996): 11231126.
Abstract (summary)
Grabens and beheaded streams above a subjacent thrust fault illuminate late Quaternary deformation
on the north limb of the Saddle Mountains anticline, Yakima fold belt, Washington. Geologic mapping
and trenches excavated across a scarp on the north flank of a 13-km-long graben and a + or -5-m-high
scarp north of the graben, confirm that deformation is related to coseismic slip on the underlying Saddle
Mountains fault. Graben development began ca. 100 ka and continued into the Holocene. At least 6.5 m
of vertical displacement in a ca. 20-40 ka paleosol yields minimum normal fault slip rates of 0.16-0.33
mm/yr. Assuming that normal slip in the hanging wall above the daylighting fault tip is related to
primary reverse slip on the fault, resolution of throw on the 30 degrees -dipping Saddle Mountains fault
yields minimum slip of 13 m and minimum slip rates of 0.33-0.65 mm/yr, 2.3-9.4 times greater than slip
rates used in a recent seismic hazard analysis for the Hanford Reservation.
d. The Saddle Mountains; the evolution of an anticline in the Yakima fold belt
Stephen P. Reidel
Rockwell Int., Geosci. Group, Richland, WA, United States
Abstract
The Saddle Mountains uplift is an asymmetrical, north vergent anticline with a length of about 110 km. It
varies from an open to tight fold and is divided into six segments based upon differences in geometry.
Flows of the Columbia River Basalt Group, intercalated sedimentary deposits of the Ellensburg
Formation, and suprabasalt sediments thin over the uplift and thicken into the synclines. Variations in
thickness are used to determine the timing of deformation and age of major and minor structures. The
close correlation of growth rate of the folds with rate of magma supply of the Columbia River Basalt
Group suggests that the Yakima fold belt resulted from the same tectonic processes that produced
eruption of the Columbia River Basalt.