Abstract: "The Tillamook map area consists of six 15' quadrangles extending from the Oregon coast eastward across the mountainous Eocene volcanic terrane of the northern Coast Range (Figure 1). The region is informally known as the Tillamook Highlands and is characterized by high rainfall, dense vegetation, and deeply weathered surface outcrops. The terrain is rugged, ranging from sea level to 3700¿¿?(1100m), but logging roads and rivers provide good access and bedrock exposure. Major forest fires in the 1930s and 1940s created spectacular exposures of the Tillamook Volcanics in the Highlands, but succesful reforestation has left only the most rugged peaks still exposed. The Tillamook map area crosses a broad, northeast-plunging structural arch in Tertiary volcanic and sedimentary strata that form the northern Oregon Coast Range (Figure 1). The core of the uplift consists of Eocene basalt and interbedded marine strata which were previously correlated with the Siletz River Volcanics of the central Oregon Coast Range (Wells and Peck, 1961). In this study, the Eocene volcanics have been divided into five units, and a distinction is made between the lower Eocene Siletz River Volcanics and the overlying Tillamook Volcanics of late middle Eocene age. Marine mudstone and sandstone are interbedded with all of the volcanic units and comprise most of the late Eocene to Miocene stratigraphic section which forms the flanks of the Coast Range uplift. Continental shelf and slope sequences predominate in the basins flanking the Coast Range uplift."
Purpose: A major goal of our investigation was to establish the basic stratigraphy and structure necessary to guide energy, mineral, hydrologic, and geologic hazard investigations in northwest Oregon. Also of interest in the Tillamook Highlands are local areas of mineralization that are concentrated in previously unrecognized silicic flows and intrusions of the Tillamook Volcanics (see map). Another important goal of this study was to determine the tectonic environment of the Eocene Tillamook Volcanics, which comprise a large part of the northern Oregon Coast Range.
Supplemental Information: scale 1:62500 "double-quoted" portions of this metadata report was taken from : Geologic Map of the Tillamook Highlands, Northwest Oregon Coast Range (Tillamook, Nehalem, Enright, Timber, Fairdale, and Blaine 15 minute Quadrangles) by Ray E. Wells1, Parke D. Snavely, Jr1, N. S. MacLeod2, Michael M. Kelly3, and Michael J. Parker4 Open File Report 94-21 1994

Progress: Complete
Update Frequency: None planned

Theme Keywords: none, geology, geoscientificInformation
Place Keywords: North America, United States of America, OR, Oregon

Access Constraints: none
Usage Constraints: see Distribution_Liability