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Geologic Setting of the Upper Klamath Basin
Prepared by:
Dane Wagner
Formation of the Upper Klamath Basin
Abstract
The Klamath Basin is located between the Cascade Mountain Range and the
Klamath Mountains. The Cascades are formed by an offshore subduction zone,
the Juan De Fuca Plate is subducting underneath the North American Plate. The
Klamath Mountains consist of exotic terrains that were amalgamated onto the
North American Plate via accretionary tectonics. The Klamath Basin is in the
northwestern most part of the basin and range province. The upper Klamath
Basin consists largely of Pleistocene lakebeds surrounded by ancient playa lake
terraces. Preliminary geologic mapping in the basin has shown that basaltic
volcanic centers are flanked by small sedimentary basins, along with active
tectonic faults.
•
•
The Upper Klamath Basin’s present position between the two mountain ranges
is in the northern most part of the Basin and Range Province. The Basin and
Range is an area of ongoing extension.
The Upper Klamath Basin thus is still experiencing extension due to the Basin
and Range. The extension is characteristic of horst-graben faulting. Faults
trend on a northwest / southeast axis.
•Faults trending in NW/SE
direction
•Faults comprised of
horsts, grabens, and
tilted fault blocks.
Introduction to the Upper Klamath
Basin
•Located between the Cascades
and the Klamath Mountain
ranges. Upper Klamath Basin is
undergoing extension due to
back arc spreading of the Basin
and Range.
•The entire Klamath Basin extends
from Southern Oregon to
Northern California, where the
Klamath River drains into the
Pacific Ocean.
•The Upper Klamath Basin is
comprised largely of Pleistocene
lakebeds that rose above present
day mash level by approximately
9 meters (Conaway 2000).
Figure 1. Upper Klamath Basin (Photo from US Fish and Wildlife, Bush 2001)
•Two stages of
deformation is thought
to occurred in faults.
• Ramping structures
• Dipslip displacement
thought to have
occurred in Pleistocene
N
Klamath Basin
•
•
Exotic terrains, composed of volcanic ach sequences, traveled hundreds of
miles from near the equator to the coast of Oregon. The terrains formed and
traveled on the Pacific Plate until they where amalgamated to the North
American Plate, creating the Klamath Mountains.
After amalgamation the terrains underwent extension to near their present
position. Today the Juan De Fuca Plate is subducting underneath the North
American Plate. The subduction of the Juan De Fuca Plate created the
Cascade Mountain Range.
Today the Upper Klamath Basin is positioned between the Klamath Mountains
on the left and the Cascades on the right.
Klamath Falls
Crater Lake
More active faults in red
•Two moderate M 5.9 and
6.0 earthquakes occurred
in 1993, approximately 30
km northwest of Klamath
Falls (Conaway, 2000).
•
The Upper Klamath Basin bedrock geology is composed mainly of Pleistocene
and Holocene basalts, with variations of lake deposits and volcanic sediment.
•
Basalts varying from largely vascular, jointed, porphyritic, and fractured. The
differing characteristics of each layer yields different aquifer conditions.
•
The variable lakebed and volcanic sediments act as confining units.
Age
Unit
Description
Water Bearing Properties
Holocene
Gravel deposits
Boulders and gravels
deposited by catastrophic
flooding. 10 m.
High permeability,
unconfined, with low yield.
Holocene
Pyroclastic deposits
Widespread unconsolidated
pumice and ash found
mantling the topography. 10
m.
High infiltration rate.
Unconfined and generally
above the water table.
Pleistocene and Holocene
Alluvium
Sands and gravels deposited
by pre-Mazama eruption
streams and rivers.
Unconfined aquifer,
recharge could move
through these deposits off
the Cascades.
Variable
Volcanic eruptive center
facies
Basaltic andesite, dacite,
Important source for
cinder, and volcanic breccia. recharge on the Cascade
Thickness is variable.
slopes
Pleistocene and Older
Younger Continental
sediments
Sandstone and diatomite
sequences. Thickness is
variable throughout the
basin (up to 120 m thick in
areas).
Serves mainly as a confining
bed.
Tertiary
Hydro-volcanics
Palagonitic rocks found at
the mouth of rivers
throughout basin .
Serves as a confining bed
for the underlying older
continental sediments.
Alternating low
permeability and high
permeability sediment
layers.
Produce high artesian yields.
Figure 3. Faults in Oregon and Upper Klamath Basin
Older Continental Sediments Sandstone, diatomite, and
clays
(Derived form Oregon Department of Geology and Mineral Industries, 2001)
Upper Klamath Basin Ancient Lakebeds and Terraces
•
Formation of the Upper Klamath Basin
•
Bedrock Geology of the Upper Klamath Basin
•
Table 2. Generalized bedrock in the Upper Klamath Basin
The Klamath Marsh is reminiscent of a ancient lake bed located in the Upper
Klamath Basin. The Klamath Marsh has experienced at least three major
fluctuations.
Each fluctuation is a recognized change in climate or surface deposits.
• The oldest lakebed formed in the Pleistocene, named Lake Chemult, and
represents pre-Mt. Mazama eruption. Contains reworked pyroclastic-fall
deposits.
• The Middle Holocene lakebed contains undisturbed pyroclastic-fall
deposits, thus meaning that the lakebed formed after the eruption of Mt.
Mazama. The Middle Holocene lakebed volume is greater than that of the
older Lake Chemult, due to a blockage of the Williamson River by a
pyroclastic flow (Conaway, 2000).
• The lowest and youngest terrace of the Late Holocene may have
developed during the early nineteen hundreds, due to agricultural
expansion (Conaway, 2000).
(Table derived from Conaway 2000)
Volcanoes of the Upper Klamath Basin
•
•
•
Basalt layers resulted from the building
of the Western Cascades and other
active volcanoes in the region.
The structures and deformation of
faults in the region has effected the
extent and placement of volcanic
centers.
Major volcanoes in the area include
• Mt. McLoughlin, Crater Lake / Mt.
Mazama, and Soloman Butte
Figure 5. Crater Lake (Photo from DOGAMI)
Conclusions
Water Level
Klamath
Marsh
99
Late Holocene
water body
289 km2
Middle
Holocene
backflooding
Diagram showing subduction
and extension in Oregon
Figure 2. Subduction Zone of the Coast of Oregon (Courtesy of NOAA/PMEL)
Extent
Pleistocene
Lake Chemult
km2
Volume
1.8 
108
m3
8.1  108 m3
•
•
•
•
The Upper Klamath Basin is comprised of far traveled terrains that where
accreted to North American Plate and then underwent extension.
Numerous faults, both active and inactive, are in the basin due to Basin and
Range extension. The faults are striking in Northwest / Southeast direction.
Basin region composed of terraces from Pleistocene and Holocene lakebeds.
Volcanic activity in region comprises the large amount of basaltic bedrock.
References Cited
560 km2
390
km2
6.5  109 m3
Not
calculated
Figure 4. Klamath Lake
Table 1. Extent and Volume of lakebeds
(Photo derived USGS)
(Chart From Conaway 2000)
Bishop, Ellen Morris. “Sunset of Upper Klamath Lake”. ONRC. 2001.
Conaway, Jeffery. “Hydrogeology and paleohydrology in the Williamson River Basin, Klamath County, Oregon”. Portland
State University. Portland, Oregon. 2000.
Hladky, Frank. “Geological Mapping in the Klamath Basin of Oregon”. Humboldt State University. Arcadia, California. 2001.
California’s Groundwater, Bulletin 118. “Upper Klamath Basin, Tule Lake Subbasin”. California Department of Water
Resources. 2004.
http://www.dpla2.water.ca.gov/publications/groundwater/bulletin118/basins/pdfs_desc/1-2.01.pdf
Oregon Department of Geology and Mineral Industries, 2001.
http://www.oregongeology.com/sub/earthquakes/oratrisk.htm
Smithsonian Institution. Global Volcanism Program, National Museum of Natural History. Washington DC. 2005.
http://www.hrw.com/science/si-science/earth/tectonics/volcano/volcano/region13/pac_ne/axial/var.html