A MODERN MAPPING OF THE SOUTHERN OREGON CASCADES

The Cascades volcanic range spans from California to Canada, and includes peaks such as Mt. Rainier and Mt. Shasta. Many of the major peaks have similar compositions of andesite and dacite, however, in southern Oregon many of the volcanoes are lower-silica basaltic and basaltic-andesite shields. Despite this distinction, the region's flows have not been well documented relative to other areas within the Cascades. This research used data previously collected by students and Prof. Stephen Crabtree, as well as preliminary field maps, to formally define the extents of volcanic units in five USGS 7.5-minute quadrangle maps in Southern Oregon. Samples’ coordinate data, geochemistries, and mineral textures were correlated to draft geologic units using the GIS software ArcMap, employing the USGS toolkit Geological Mapping Schema (GeMS). The resulting maps allow a better understanding of the extents of major units such as Blue Rock and Rustler Peak, and interstitial minor units. Boundaries were clarified as being visible or inferred contacts, allowing more confidence in determining units’ eruptive sequences, despite the lack of abundant geochronology data. The mapping provides more clarity to geologic units in Southern Oregon, using modern methods and software to build upon existing data and past mapping techniques.