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International Geology Review Vol 51 Nos 9 11 September November 2009 777 823 Cenozoic palaeocanyon evolution Ancestral Cascades arc volcanism and structure of the Hope Valley Carson Pass region Sierra Nevada California Jeanette C Hagana Cathy J Busbya Keith Putirkab and Paul R Rennecd a Department of Earth Science University of California Santa Barbara Santa Barbara CA 93106 USA bDepartment of Earth and Environmental Sciences California State University Fresno CA 93710 USA cBerkeley Geochronology Center 2455 Ridge Rd Berkeley CA 94709 USA d Department of Earth and Planetary Science University of California Berkeley CA 94720 USA Accepted 20 April 2009 We use new geologic mapping geochronological and geochemical data on Tertiary volcanic volcaniclastic and intrusive rocks to investigate the volcanic stratigraphic and structural evolution of the Carson Pass region south of Lake Tahoe in the central Sierra Nevada Volcanic and volcaniclastic rocks were deposited in east west trending palaeocanyons carved into Mesozoic granitic and metamorphic basement rocks sediments were transported westwards towards the present day Central Valley of California In the Carson Pass Hope Valley area two palaeotributaries are preserved in faulted terrane east of the present day Sierran crest Hope Valley area these merge at the crest to form one large 7 km wide palaeocanyon that is undisrupted by faults west of the crest Carson Pass Kirkwood area This single large palaeocanyon roughly coincides with the present day Mokelumne River drainage New 40Ar 39Ar dates and stratigraphic data east of the crest integrated with previously published data west of the crest constrain the ages of strata and unconformities within the Hope Valley Carson Pass Kirkwood palaeocanyon system We interpret three major erosional unconformities to record uplift events at ca 23 16 13 5 11 and 10 7 Ma In other parts of the central Sierra these uplift events are inferred to correspond to range front faulting events We

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