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The Stratigraphy And Structure Of The Columbia River Basalt Group In The Bull Run Watershed, Multnomah And Clackamas Counties, Oregon, Beverly Frobenius Vogt

Dissertations and Theses

Approximately 150 meters (500 feet) of Grande Ronde Basalt and 140 meters (450 feet) of Wanapum Basalt of the Columbia River Basalt Group are exposed in the Bull Run Watershed. In Bull Run, the Grande Ronde Basalt is divided into three mappable units: "low Mg" R₂ (at least one flow), "low Mg" N₂ (approximately four flows), and "high Mg" N₂ (two to three flows}. The Wanapum Basalt is represented by two members: Frenchman Springs Member (six flows) and Priest Rapids Member (one flow). These units are identified by instrumental neutron activation analysis, paleomagnetism based on measurements with …