Abstract

1
Geologic Setting of the Upper Klamath
Basin Prepared by Dane Wagner

• Formation of the Upper Klamath Basin
• The Upper Klamath Basins 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.

• Bedrock Geology of the Upper Klamath Basin
• 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.

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.

• Faults trending in NW/SE
• direction
• Faults comprised of
• horsts, grabens, and
• tilted fault blocks.
• Two stages of
• deformation is thought
• to occurred in faults.
• Ramping structures
• Dipslip displacement
• thought to have
• occurred in Pleistocene
• Two moderate M 5.9 and
• 6.0 earthquakes occurred
• in 1993, approximately 30
• km northwest of Klamath

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, cinder, and volcanic breccia. Thickness is variable. Important source for recharge on the Cascade 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.
Older Continental Sediments Sandstone, diatomite, and clays Alternating low permeability and high permeability sediment layers. Produce high artesian yields.

• 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).

N
More active faults in red
Klamath Basin Klamath Falls Crater
Lake
Figure 3. Faults in Oregon and Upper Klamath
Basin (Derived form Oregon Department of
Geology and Mineral Industries, 2001)

• Upper Klamath Basin Ancient Lakebeds and Terraces
  
• 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 2. Generalized bedrock in the Upper
Klamath Basin (Table derived from Conaway 2000)
Figure 1. Upper Klamath Basin (Photo from US Fish
and Wildlife, Bush 2001)

• 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

• Formation of the Upper 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.

Figure 5. Crater Lake (Photo from DOGAMI)

• Conclusions
• 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.

Water Level Extent Volume
Klamath Marsh 99 km2 1.8 108 m3
Late Holocene water body 289 km2 8.1 108 m3
Middle Holocene backflooding 560 km2 6.5 109 m3
Pleistocene Lake Chemult 390 km2 Not calculated
References Cited 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.
Californias Groundwater, Bulletin 118. Upper
Klamath Basin, Tule Lake Subbasin. California
Department of Water Resources. 2004. http//www.d
pla2.water.ca.gov/publications/groundwater/bulleti
n118/basins/pdfs_desc/1-2.01.pdf Oregon
Department of Geology and Mineral Industries,
2001. http//www.oregongeology.com/sub/earthquake
s/oratrisk.htm Smithsonian Institution. Global
Volcanism Program, National Museum of Natural
History. Washington DC. 2005. http//www.hrw.co
m/science/si-science/earth/tectonics/volcano/volca
no/region13/pac_ne/axial/var.html
Diagram showing subduction and extension in
Oregon
Figure 4. Klamath Lake Table 1. Extent and
Volume of lakebeds (Photo derived USGS) (Chart
From Conaway 2000)
Figure 2. Subduction Zone of the Coast of Oregon
(Courtesy of NOAA/PMEL)