Columbia River Basalt 87 SERIES GROUP SUB-GROUP FORMATION MEMBER K-Ar AGE (m.y) MAGNETIC POLARITY MIocene UPPER 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 WILBUR CREEK MEMBER Basalt of Lapwai N Basalt of Wahluke N UMATILLA MEMBER Basalt of Sillusi N Basalt of Umatilla N LOCAL EROSIONAL UNCONFORMITY PRIEST RAPIDS MEMBER 14.5 R Basalt of Lolo R Basalt of Rosalia ROZA MEMBER T, R FRENCHMAN SPRINGS MEMBER 15.3 N Basalt of Lyons Ferry N Basalt of Sentinel Gap N Basalt of Sand Hollow N,E Basalt of Silver Falls 15.5 E Basalt of Ginkgo Basalt of Palouse Falls ECKLER MOUNTAIN MEMBER Basalt of Shumaker Creek N Basalt of Dodge N Basalt of Robinette Mountain N N2 GRANDE RONDE R2 PICTURE GORGE BASALT (See Mangan and others, 1986; Reidel, 1983 for individual flows) 15.6-16.5 N1 BASALT R1 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=excursionall.