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Scientific Investigations Report 2007–5050

Scientific Investigations Report 2007–5050
Version 1.1, April 2010

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Table 1. Generalized hydrogeologic units in the upper Klamath Basin, Oregon and California.

Hydrogeologic unit Map symbol Lithologic and hydrologic characteristics
Quaternary sedimentary deposits Qs Fine- to coarse-grained sediments deposited in stream valleys and major lake basins. Permeable coarse-grained deposits occur in stream valleys and locally in the lake basins. The lake basin deposits are, however, predominantly fine grained and have low permeability.
Quaternary volcaniclastic deposits Qvp Pyroclastic flows and air fall material (pumice, ash, and lapilli) deposited during the climactic eruption of Mt. Mazama that formed Crater Lake, and debris avalanche deposits of the Shasta River Valley. Air fall deposits are highly permeable. Pyroclastic flows and debris deposits may have low permeability.
Quaternary volcanic rocks Qv Basaltic and andesitic lavas and vent deposits occurring in the Cascade Range and around Medicine Lake Volcano. These materials are generally highly permeable, but may not be saturated at high elevations.
Quaternary to late Tertiary sedimentary rocks QTs Fine- to coarse-grained unconsolidated to moderately indurated sedimentary deposits. The hydraulic characteristics of this unit are not well known but lithologic descriptions on maps suggest it may be moderately permeable at some locations. This unit has very limited distribution.
Late Tertiary sedimentary rocks Ts Predominately fine-grained continental sedimentary deposits including bedded diatomite, mudstone, siltstone, and sandstone. This unit has generally low permeability but contains permeable strata at some locations.
Late Tertiary volcaniclastic rocks Tvpt Palagonitized basaltic ash and lapilli deposits associated with eruptive centers. The hydrologic characteristics of this unit are not well known, but springs are known to emerge from basal contact with unit Ts. This unit is most prominent in the Sprague River valley.
Late Tertiary volcanic rocks Tv Predominantly basaltic and andesitic lava flows and vent deposits with lesser amounts of silicic domes and flows. This unit has moderate to high permeability and is by far the most widely developed aquifer unit in the study area. Permeability is locally diminished by hydrothermal alteration and secondary mineralization.
Older Tertiary volcanic and sedimentary rocks Tovs Miocene and older volcanic and volcaniclastic deposits. The permeability of this unit is generally low due to weathering, hydrothermal alteration, and secondary mineralization. This unit is generally considered a boundary to the regional ground-water system of the upper Klamath Basin.

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