Columbia River Basalt 87 SERIES GROUP SUB- GROUP FORMATION MEMBER K-Ar AGE (m.y.) MAGNETIC POLARITY MIocene UPPER BASALT SADDLE LOWER MONUMENTAL MEMBER 6 N EROSIONAL UNCONFORMITY ICE HARBOR MEMBER 8.5 Basalt of Goose Island Basalt of Martindale Basalt of Basin City 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 N ASOTIN MEMBER 13 N Basalt of Huntzinger LOCAL EROSIONAL UNCONFORMITY WILBUH CREEK MEMBER Basalt of Lapwal Basalt of Wahluke N UMATILLA MEMBER Basalt of Siliusl Basalt of Umatilla N N LOCAL EROSIONAL UNCONFORMITY PRIEST RAPIDS MEMBER 14.5 R R < Basalt of Lolo Basalt of Rosalia 380 ROZA MEMBER T, R FRENCHMAN SPRINGS MEMBER 15.3 N Basalt of Lyons Ferry Basalt of Sentinel Gap Basalt of Sand Hollow Basalt of Silver Falls Basalt of Ginkgo Basalt of Palouse Falls N, E E ECKLER MOUNTAIN MEMBER N Basalt of Shumaker Creek Basalt of Dodge Basalt of Robinette Mountain N GRANDE RONDE (See Mangan and others, 1986; Reidel, 1983 for individual flows) 15.6-16.5 N2 R2 PICTURE GORGE BASALT Basalt N1 R1 IMNAHA BASALT (See Hooper and others, 1984) 16.5-17.0 R1 T No Ro 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-excursiona.