Location of mapped area (dotted lines on the two maps):

Geologic Overview

The area of the Klamath Falls geologic map lies east of the High Cascades at the south end of Upper Klamath Lake. The Klamath River provides the main drainage from the area, flowing from Upper Klamath Lake to the Pacific Ocean. The map boundaries encompass the urban growth boundary for the City of Klamath Falls plus some fringing areas. The map covers all of the Klamath Falls and Altamont topographic quadrangles, ~20 percent of the Wocus quadrangle, and ~10 percent of the adjacent Whiteline Reservoir quadrangle to the northeast.

Situated in the extreme northwestern part of the Basin and Range province, the quadrangle is dominated by the horst and graben topography resulting from the extensional tectonics that characterize the Basin and Range of southeast Oregon. Elevation in the area ranges from 4,073 feet (1,240 m) at the Lost River to 6,200 feet (1,890 m)at the top of Hogback Mountain. The northwest-trending normal faults that bound Upper Klamath Lake and form the Klamath graben expose up to 480 m of volcanic and sedimentary rocks, ranging in age from late Miocene to Holocene. Upper Klamath Lake and surficial deposits of lake and river sediment cover approximately 25 percent of the map area. Link River flowing out of Upper Klamath Lake and the Klamath River flowing out of Lake Ewauna form the main perennial stream system in the area. The Lost River is a smaller river that flows on the southeastern side of the map area.

Rock in the area is chiefly ~2-7 Ma dark gray lava (basalt and basaltic andesite) and contemporaneous to younger cream-colored diatomaceous mudstone. Local outcrops of sandstone and conglomerate cap a few low hills between Oregon Institute of Technology (OIT) and the Stewart Lennox area. Andesite crops out in a few areas near Link River, Stewart Lennox, and the southeastern tip of Hogback Mountain. Rocks in the area are the product of complex interaction between sedimentation and Cascade volcanism. Composition and extent of the volcanic rocks was modified after ~4 Ma by Basin and Range extension and the decreasing width of Cascade volcanic arc. By the time of the Pleistocene glaciations (by ~1.6 Ma) Cascade volcanic activity had mostly ceased in the area, as Cascade volcanism continued to narrow toward its present location in the High Cascades. Basin and Range extension continued to pull the area apart, dropping basins lower relative to ridges like Hogback Mountain, while sedimentation, helped along by periodic ash fall from the High Cascades, filled lake basins like Upper Klamath Lake and Round Lake.

Geothermal Resources

Included in the text of the report and illustrated below are figures showing areas of highest temperature groundwater and highest temperature gradients. These areas may have high potential for extraction of geothermal energy.

Well temperatures for the mapped area (in degrees Centigrade); red areas indicate where wells have intercepted rock at temperatures greater than 82°C (180°F), a temperature useful for direct-use geothermal heating applications. The fact that a well has a relatively low temperature does not mean that the area lacks higher temperatures. The well may be a shallow well that never reached deep enough to be hot. See the map below for how quickly temperature increases with depth in the area. Some of the data points have more than one well in a small area, but a temperature label for only one of the wells will show in this map view of the data; that temperature may or may not be the highest one in that area. The areas highlighted in red take into account the highest temperature wells for each such area of closely spaced wells. Warmer colors on the base map indicate higher elevations; Ore. Inst. Tech. is Oregon Institute of Technology.

Geothermal gradients and faults in the map area. Gradients are contoured at intervals of 50°C/km. Faults may be areas of higher fracturing of rock units, leading to higher permeability and more likelihood of good flow of geothermal fluid. Brittle rock units like lava flows, sandstone, conglomerate, and silicified (quartz-flooded) rocks are more likely to have open fractures that carry water. Hot water is more likely to be found at shallow depth in areas where temperature gradients are high. Good geologic reasoning based on detailed, site-specific geological and geophysical data should be used to infer where and at what depth faults intercept brittle rocks. Faults shown as red lines cut rocks with approximate age of 1.8 million years; faults shown as black lines cut older rocks.

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