Condrey Mountain Schist Type Section Geologic Area
Condrey Mountain Schist Type Section, along roadcut.
Condrey Mountain Schist Type Section Geologic Area is located on the south bank of the Klamath River, along county road 8G004. The seventy (70) foot high rock outcrop is located along the roadside near a sharp curve. Poison Oak thrives along the base of the outcrop and is pervasive in the wooded area. Please use caution.
Geologic Background
The Condrey Mountain Schist is a major metamorphic rock unit in the Klamath Mountains. It outcrops throughout the California—Oregon region and has an aerial coverage of at least 250 square miles. This area was designated by geologist Preston Hotz as a geologic type section; meaning that it is a representative outcrop of the entire rock unit, providing a basis of comparison for future geologic mapping and interpretation.
Based on extensive investigations, the Condrey Mountain Schist is interpreted to represent a slice of ancient seafloor. Its lithologic sequence includes metamorphosed volcanic rocks, deep water sediments and organic matter.
Geologic Processes at Work
Any rock that has been affected by an increase in heat or pressure is called a metamorphic rock. Schist is a type of metamorphic rock that is characterized by certain mineral constituents (including mica, talc, chlorite, feldspar, quartz) and exhibits mineral alignment, or “foliation”, allowing the schist to be split apart easily.
The process of subduction caused an increase in pressure and temperature, which resulted in the recrystallization and metamorphism of minerals in the rocks. Microscopic mineral analysis indicates that the Condrey Mountain Schist endured high pressures and temperatures as it was thrust up with the rest of the Klamath Mountains.
Rubbing the rock from this outcrop leaves a slick black film on your fingers. This is the result of the metamorphic mineral graphite, which formed from the metamorphosed remains of organisms. Graphite behaves like a lubricant, similar to talcum powder. Its presence here reduces frictional resistance to landsliding and makes hill slopes unstable.
View of the asphalt in front of the graphite-rich Condrey Mountain Schist roadcut.
The photo shows road–cracks: This evidence of slope instability may be the result of the graphite–rich Condrey Mountain Schist which underlies the road at this location. Additionally, pencil “lead” is actually a polymer composite containing graphite.
References
Hotz, P.E., 1979, Regional metamorphism in the Condrey Mountain quadrangle, north–central Klamath Mountains, California: US Geological Survey Professional Paper 1086.
Helper, M.A., 1985. Structural, metamorphic and geochronologic constraints on the origin of the Condrey Mountain Schist, north central Klamath Mountains, northern California [Ph.D thesis]: University of Texas at Austin, 209 p.
Helper, M.A., 1986. Deformation and high P/T metamorphism in the central part of the Condrey Mountain window, north–central Klamath Mountains, California and Oregon. Geological Society of America, Memoir 164.