Klamath Basin
The Klamath Basin is the region in the U.S. states of Oregon and California drained by the Klamath River. It contains most of Klamath County and parts of Lake and Jackson counties in Oregon, and parts of Del Norte, Humboldt, Modoc, Siskiyou, and Trinity counties in California. The 15,751-square-mile (40,790 km2) drainage basin is 35% in Oregon and 65% in California. In Oregon, the watershed typically lies east of the Cascade Range, while California contains most of the river's segment that passes through the mountains. In the Oregon-far northern California segment of the river, the watershed is semi-desert at lower elevations and dry alpine in the upper elevations. In the western part of the basin, in California, however, the climate is more of temperate rainforest, and the Trinity River watershed consists of a more typical alpine climate.
The Upper Klamath Watershed lies between the Cascade Range and the Basin and Range Province in southern Oregon and northern California. Bedrock stratigraphy in the area includes volcanic deposits, volcanic ejecta, and fluviolacustrine deposits. This creates three general hydrologic layers: 1) Highly permeable basalt with an older depositional age serving as the principle aquifer, 2) fluvial deposits made up of tuff, shale, agglomerate, sandstone, and volcanic ash that are collectively known as the Yonna Formation and act as a groundwater cap, and 3) more recent eruptive volcanic deposits that overlie the aquifer. Little water is able to permeate through the upper volcanic deposit layers to the principle aquifers. Groundwater is able to move freely throughout the upper basin despite geologic structures that occur due to normal faulting which only confine groundwater on a local scale.Artesian wells discharging into the Upper Klamath Lake are essential for recharge into the lake and Klamath River flow throughout the year. Snowmelt is currently a large contributor of groundwater recharge in the Upper Klamath Basin.
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