Columbia River Basalt 87 SERIES GROUP SUB-GROUP FORMATION MEMBER K-Ar AGE (m.y) MAGNETIC POLARITY MIOCENE UPPER MIDDLE BASALT COLUMBIA RIVER YAKIMA SADDLE LOWER BASALT MOUNTAINS BASALT LOWER MONUMENTAL MEMBER 6 N EROSIONAL UNCONFORMITY ICE HARBOR MEMBER 8.5 Basalt of Goose Island N Basalt of Martindale R Basalt of Basin City N EROSIONAL UNCONFORMITY BUFORD MEMBER R ELEPHANT MOUNTAIN MEMBER 10.5 R T EROSIONAL UNCONFORMITY POMONA MEMBER 12 R EROSIONAL UNCONFORMITY ESQUATZEL MEMBER N EROSIONAL UNCONFORMITY WEISSENFELS RIDGE MEMBER Basalt of Slippery Creek N Basalt of Tenmile Creek N Basalt of Lewiston Orchards N Basalt of Cloverland N ASOTIN MEMBER 13 N Basalt of Huntzinger LOCAL EROSIONAL UNCONFORMITY WILBUH CREEK MEMBER Basalt of Lapwal N Basalt of Wahluke N UMATILLA MEMBER Basalt of Sillust N Basalt of Umatilla N LOCAL EROSIONAL UNCONFORMITY PRIEST RAPIDS MEMBER 14.5 R Basalt of Lolo R Basalt of Rosalia 13.0 ROZA MEMBER T, R FRENCHMAN SPRINGS MEMBER 15.3 Basalt of Lyons Ferry N Basalt of Sentinel Gap N Basalt of Sand Hollow N Basalt of Silver Falls N, E Basalt of Ginkgo E Basalt of Palouse Falls E ECKLER MOUNTAIN MEMBER Basalt of Shumaker Creek N Basalt of Dodge N Basalt of Robinette Mountain N GRANDE RONDE N2 R2 PICTURE GORGE BASALT (See Mangan and others, 1986; Reidel, 1983 for individual flows) 15.6-16.5 N1 R1 BASALT IMNAHA BASALT (See Hooper and others, 1984) 16.5-17.0 R1 T N0 R0 Figure 2. Stratigraphy of the Columbia River Basalt Group. Modified from Swanson and others (1979) by Reidel and Fecht (1987). Natural remanent magnetization indicated by: N=normal, R=reversed, T-transitional, and E=excursional. cf. Reidel, S.P. and Fecht, K.R. 1982. The Huntzinger Flow: evidence of surface mixing of the Columbia River Basalt and its petrogenetic implications. Geol. Soc. Amer. Bull. 93:664-677.