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Geologic map of the Beacon Rock quadrangle, Skamania County, Washington

Scientific Investigations Map 3367

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and
https://doi.org/10.3133/sim3367

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Abstract

The Beacon Rock 7.5′ quadrangle is located approximately 50 km east of Portland, Oregon, on the north side of the Columbia River Gorge, a scenic canyon carved through the axis of the Cascade Range by the Columbia River. Although approximately 75,000 people live within the gorge, much of the region remains little developed and is encompassed by the 292,500-acre Columbia River Gorge National Scenic Area, managed by a consortium of government agencies “to pro­tect and provide for the enhancement of the scenic, cultural, recreational and natural resources of the Gorge and to protect and support the economy of the Columbia River Gorge area.” As the only low-elevation corridor through the Cascade Range, the gorge is a critical regional transportation and utilities corridor (Wang and Chaker, 2004). Major state and national highways and rail lines run along both shores of the Columbia River, which also provides important water access to ports in the agricultural interior of the Pacific Northwest. Transmission lines carry power from hydroelectric facilities in the gorge and farther east to the growing urban areas of western Oregon and Washington, and natural-gas pipelines transect the corridor (Wang and Chaker, 2004). These lifelines are highly vulnerable to disruption by earthquakes, landslides, and floods. A major purpose of the work described here is to identify and map geologic hazards, such as faults and landslide-prone areas, to provide more accurate assessments of the risks associated with these features.

The steep canyon walls of the map area reveal exten­sive outcrops of Miocene flood-basalt flows of the Columbia River Basalt Group capped by fluvial deposits of the ances­tral Columbia River, Pliocene lavas erupted from the axis of the Cascade arc to the east, and volcanic rocks erupted from numerous local vents. The Columbia River Basalt Group unconformably rests on a sequence of late Oligocene and early Miocene rocks of the ancestral Cascade volcanic arc, which underlies most of the map area. The resistant flood-basalt flows form some of the famous landforms in the map area, such as Hamilton Mountain. Extensive landslide complexes have devel­oped where the basalt flows were emplaced on weak volcani­clastic rocks.

Suggested Citation

Evarts, R.C., and Fleck, R.J., 2017, Geologic map of the Beacon Rock quadrangle, Skamania County, Washington: U.S. Geological Survey Scientific Investigations Map 3367, pamphlet 61 p., scale 1:24,000, https://doi.org/10.3133/sim3367.

ISSN: 2329-132X (online)

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Additional publication details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Geologic map of the Beacon Rock quadrangle, Skamania County, Washington
Series title:
Scientific Investigations Map
Series number:
3367
DOI:
10.3133/sim3367
Year Published:
2017
Language:
English
Publisher:
U.S. Geological Survey
Publisher location:
Reston, VA
Contributing office(s):
Geology, Minerals, Energy, and Geophysics Science Center
Description:
Pamphlet: ii, 61 p.; 2 Sheets: 53.90 x 37.06 inches and 61.75 x 31.64 inches; Basemap: 24.00 x 30.00 inches; Database; Metadata; Read Me
Country:
United States
State:
Washington
County:
Skamania County
Other Geospatial:
Beacon Rock quadrangle
Online Only (Y/N):
Y