Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey

Scientific Investigations Report 2017-5022-H
By: , and 



The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disruption, and forest fires. Although the focus of this multidisciplinary field trip will be on mafic volcanism, we will also look at the hydrology, geomorphology, and ecology of the area, and we will examine how these elements both influence and are influenced by mafic volcanism. We will see mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. In addition, this field trip will occur during a total solar eclipse, the first one visible in the United States in more than 25 years (and the first seen in the conterminous United States in more than 37 years).

The Cascade Range is the result of subduction of the Juan de Fuca plate underneath the North American plate. This north-south-trending volcanic mountain range is immediately downwind of the Pacific Ocean, a huge source of moisture. As moisture is blown eastward from the Pacific on prevailing winds, it encounters the Cascade Range in Oregon, and the resulting orographic lift and corresponding rain shadow is one of the strongest precipitation gradients in the conterminous United States. We will see how the products of the volcanoes in the central Oregon Cascades have had a profound influence on groundwater flow and, thus, on the distribution of Pacific moisture. We will also see the influence that mafic volcanism has had on landscape evolution, vegetation development, and general hydrology.

Suggested Citation

Deligne, N.I., Mckay, D., Conrey, R.M., Grant, G.E., Johnson, E.R., O’Connor, J., and Sweeney, K., 2017, Field-trip guide to mafic volcanism of the Cascade Range in central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey: U.S. Geological Survey Scientific Investigations Report 2017–5022–H, 94 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Preface
  • Contributing Authors
  • Abstract
  • Introduction and Trip Overview
  • A Brief Overview of the Geologic and Physiographic Setting of the Cascade Range
  • Day 1: Portland to H.J. Andrews Experimental Forest (Near the Town of Blue River)
  • Day 2: H.J. Andrews Experimental Forest to Bend, by Way of the Sand Mountain Volcanic Field
  • Day 3: Total Solar Eclipse and Various Stops in the Bend Area
  • Day 4: The McKenzie Pass Area
  • Day 5. The Bend Area
  • Day 6. Bend to Portland
  • Acknowledgments
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey
Series title Scientific Investigations Report
Series number 2017-5022
Chapter H
DOI 10.3133/sir20175022H
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Volcano Science Center
Description xii, 94 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Field-trip guides to selected volcanoes and volcanic landscapes of the western United States (Scientific Investigations Report 2017-5022)
Country United States
State Oregon
Other Geospatial Cascade Range
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details