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REPORT:
Guide to Geologic Field Trip Between Lewiston, Idaho, and Kimberly, Oregon, Emphasizing the Columbia River Basalt Group


-- Swanson, D.A., and Wright, T.L., 1981,
Guide to Geologic Field Trip Between Lewiston, Idaho, and Kimberly, Oregon, Emphasizing the Columbia River Basalt Group: IN: Johnston, D.A., and Donnelly-Nolan, J., (eds.), 1981, Guides to Some Volcanic Terranes in Washington, Idaho, Oregon, and Northern California: U.S. Geological Survey Circular 838, 189p.

Columbia River Basalt Group
Series Group Subgroup Formation Member K-Ar Age
(million years) 		Magnetic Polarity
M
I
O
C
E
N
E 		U
p
p
e
r

M
i
o
c
e
n
e 		Columbia
River
Basalt
Group 		Yakima
Basalt
Subgroup 		Saddle Mountains Basalt Lower Monumental Member 6 N
Erosional Unconformity
Ice Harbor Member 8.5 N
8.5 R
8.5 N
Erosional Unconformity
Buford Member   R
Elephant Mountain Member 10.5 N, T
M
i
d
d
l
e

M
i
o
c
e
n
e 		Erosional Unconformity
Pomona Member 12 R
Erosional Unconformity
Esquatzel Member   N
Erosional Unconformity
Wessenfels Ridge Member   N
  N
Asotin Member   N
Local Erosional Unconformity
Wilber Creek Member   N
Umatilla Member   N
Local Erosional Unconformity
Wanapum Basalt Priest Rapids Member   R
Roza Member   R, T
Frenchman Springs Member   N
Eckler Mountain Member   N
  N
  N
L
o
w
e
r

M
i
o
c
e
n
e 		Grand Ronde Basalt

Picture Gorge Basalt
  14-16.5

14.6-15.8
N
R
  N
R
Imnaha Basalt     R
T
N
R, ?
K-Ar age from McKee and others (1977) and Watkins and Baksi (1974). N, normal magnetic polarity; R, reversed; T, transitional. Geologic time scale from Berggren and Van Couvering (1974). The Imnaha and Picture Gorge Basalts are nowhere known to be in contact. Interpretation of preliminary magnetostratigraphic data suggests that the Imnaha is everywhere older than the Picture Gorge. See Swanson and Wright (1981). Modified from Swanson and others (1979b).
Lyn Topinka, 1998, Modified from: Swanson and Wright, 1981, IN: Johnston and Donnelly-Nolan, 1981, USGS Circular 838

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06/20/02, Lyn Topinka