Abstract
An area of unmapped intrusions lies within the Bull-of-the-Woods Roadless Area of Mount Hood National Forest. A variety of andesites, dacites,and diorites intruding units of tuff and andesite lava flows crop out over.an area of 52 sq km. These intrusions do not appear on the Geologic Map of Oregon West of the 121st Meridian (Hells and Peck, 1961). The purpose of this investigation is to map and describe these intrusions, with attention to the following questions: What is the petrographic and geochemical nature of these intrusions? What is the order of emplacement of these intrusions? What is the probable mechanism of intrusion? What relation do these intrusions bear to a possible underlying batholith? Contact relations in the field, petrographic studies, and major and trace element trends were used to address these questions.
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