Beheaded west-flowing drainages in the Lake Tahoe region, northern Sierra Nevada: implications for timing and rates of normal faulting, landscape evolution and mechanism of Sierran uplift

Abstract

Beheaded west-flowing drainages are identified in the northern Sierra Nevada west and north of the Lake Tahoe Basin. These include the canyons of the modern South Fork American River, the Rubicon River, the South Yuba River and their tributaries. These drainages were beheaded, east-side-down displacements along faults of the Tahoe-Sierra frontal fault zone as Cenozoic normal faults encroached into the Sierra Nevada block about 2.5–3 Ma. Most major Sierran passes in this region are wind gaps or water gaps formed by beheading, and include Carson Pass, Echo Summit, Aloha Pass, Velma Lakes Pass, Miller Creek Pass, Five Lakes Pass, Donner Pass and Euers Saddle. The Carson Range represents a remnant of the former Sierran crestal region, and may have formerly attained elevations between 3.6 and 4 km. Possible remnants of the beheaded west-flowing Sierran drainages occur as major passes in the Carson Range and include passes at Big Meadows, Luther Pass, Armstrong Pass, Star Pass, Daggett Pass, Spooner Summit and Tahoe Meadows. Several possible remnants of a tributary of the modern Rubicon River, Five Lakes Creek, are preserved in mountainous areas along the north edge of Lake Tahoe. Carson Range faults beheaded many of the drainage remnants, indicating that the ∼3 Ma Sierran drainage divide lay somewhat east of the present crest of the Carson Range. Speculative reconstructions of the former South Fork American, Rubicon and South Yuba drainages, along with other regional data, provide constraints on timing and rates of uplift, tilting and normal faulting, and support recent concepts about mechanisms of late Cenozoic Sierran uplift.