Columbia River Basalt 87 SERIES GROUP SUB-GROUP FORMATION MEMBER K-Ar AGE (m.y) MAGNETIC POLARITY MIOCENE UPPER GROUP SUBGROUP LOWER MONUMENTAL MEMBER 6 N EROSIONAL UNCONFORMITY ICE HARBOR MEMBER Basalt of Goose Island Basalt of Martindale Basalt of Basin City 8.5 N R 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 Basalt of Tenmile Creek Basalt of Lewiston Orchards Basalt of Cloverland N N N ASOTIN MEMBER Basalt of Huntzinger 13 N LOCAL EROSIONAL UNCONFORMITY WILBUH CREEK MEMBER Basalt of Lapwal Basalt of Wahluke N UMATILLA MEMBER Basalt of Sillius Basalt of Umatilla N LOCAL EROSIONAL UNCONFORMITY PRIEST RAPIDS MEMBER Basalt of Lolo Basalt of Rosalla 14.5 R ROZA MEMBER T, R FRENCHMAN SPRINGS MEMBER Basalt of Lyons Ferry Basalt of Sentinel Gap Basalt of Sand Hollow Basalt of Silver Falls Basalt of Ginkgo Basalt of Palouse Falls 15.3 N N N, E E 15.5 E ECKLER MOUNTAIN MEMBER Basalt of Shumaker Creek Basalt of Dodge Basalt of Robinette Mountain N N N GRANDE RONDE PICTURE GORGE BASALT (See Mangan and others, 1986; Reidel, 1983 for individual flows) 15.6-16.5 N2 R2 N1 BASALT R1 Musselshell Julietta 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=excursion. cf. REIDEL, S.P. AND FECHT, K.R. 1986. THE HUNTZIGER FLOW: evidence of surface mixing of The Columbia River Basalt and its petrogenetic implications. Geol. Soc. Amer. Bull. 98: 664-672.