The Frenchman Springs Member is the most voluminous member of the Wanapum Basalt, Columbia River Basalt Group. We have revised the distribution maps and estimates of the areas and volumes for the units of the Frenchman Springs based on mapping and fieldwork that have been conducted since the previous compilation in 1989. The revised estimates indicate that many of the Frenchman Springs flows are significantly larger than previously believed. The total area underlain by Frenchman Springs flows is now estimated to be ~72,595 km 2 ; the revised volume is estimated to be ~7628 km 3 . Based on the new data, the Basalts of Palouse Falls, Ginkgo, Sand Hollow, and Sentinel Gap are significantly more voluminous than previously indicated, while the Basalt of Silver Falls is significantly smaller. We have also reduced the number of units within the Frenchman Springs Member to five. The Basalt of Lyons Ferry has been combined with the Basalt of Sentinel Gap based on the similarity of their geochemistries and paleomagnetism and the lack of an identified dike/vent system. Geochemical variations in Frenchman Springs Member flows (as well as those in the Roza and Priest Rapids Members, Wanapum Basalt) are consistent with being produced by open magma system processes.

Nearly twenty flows of the Columbia River Basalt Group (CRBG) can be paleomagnetically and chemically correlated westward as far as 500 km from the Columbia Plateau in Washington, through the Columbia Gorge, to the Coast Range of Oregon and Washington. In the Coast Range near Cathlamet, Washington, the CRBG flow stratigraphy includes 10 flows of Grande Ronde Basalt (1 low-MgO R 2 flow, 6 low-MgO N 2 flows, 3 high-MgO N 2 flows), 2 flows of Wanapum Basalt (both flows of Sand Hollow from the Frenchman Springs Member), and the Pomona Member of the Saddle Mountains Basalt. Elsewhere in the Coast Range, additional Grande Ronde Basalt flows, including flows of Winterwater or Umtanum, and additional Wanapum flows, including the flows of Ginkgo, have been reported. Thus at least 18 to 20 CRBG flows reached the coast region. Several of these distal flows have distinctive chemical and magnetic characteristics that are shared by nearby isolated intrusions in Coast Range sedimentary rocks, thus strongly supporting recent suggestions that these intrusions are invasive bodies fed by CRBG flows. Magnetization directions from several flows indicate 16 to 30° of clockwise rotation of the coast with respect to the plateau since middle Miocene time.