Taylorsville sequence and lower Lake Tahoe sequence
Taylorsville sequence and lower Lake Tahoe sequence
Pennsylvanian to Late Devonian
Consists mainly of: (1) Devonian Grizzly Formation (conglomerate, sandstone, slate, and minor chert and limestone), gradationally overlain by (2) Devonian Sierra Buttes Formation (quartz-rich felsic tuff, tuff breccia, and minor rhyolite, dacite, and andesite intrusive rocks); (3) Mississippian Taylor Formation (andesite flows, tuff breccia, tuff, and tuffaceous turbidites); and (4) Mississippian and Pennsylvanian Peale Formation (chert and minor siliceous argillite, felsic tuff, tuff breccia, flows, and volcaniclastic sandstone and siltstone, and basalt, latite, rhyolite volcanic, and volcaniclastic rocks). These units crop out in several structural blocks between the northern margin of the Sierra Nevada and the Middle Fork American River. East of Talbot fault, this unit (locally named the Lake Tahoe sequence) includes (1) Devonian and Mississippian Picayune Valley (black slate, quartzite, chert-clast conglomerate, limestone, felsic tuff, felsic lahar deposits, and andesitic tuff breccia), (2) Mississippian or younger Serena Creek (recrystallized ribbon chert and minor black siliceous argillite), and (3) Mississippian(?) or younger(?) Onion Creek (limestone, quartzite, and calc-silicate rock) Formations (Harwood, 1992; Harmon, 2015).
In the northwesternmost block (Butt Valley block of Jayko, 1990), this unit lacks geochronologic control but is composed of pyroxene-bearing metaandesite assigned to the Taylor Formation (D’Allura and others, 1977), unconformably overlain by Triassic and Jurassic strata (part of unit NSST). The base of the unit there is faulted. 
Farther east, the full sequence unconformably overlies (and is intruded by) Devonian plutonic rocks (unit Gsb) and the Shoo Fly Complex (unit NSSA), and is in turn unconformably overlain by the Permian volcanic sequence (unit NSRO), although the Grizzly Formation is limited in extent and missing at the base of the sequence in many areas. The Grizzly Formation north of the North Yuba River has yielded Frasnian (early Late Devonian) corals and gastropods and middle Famennian conodonts, which are also found on the Middle Yuba River (Hanson and Schweickert, 1986; Harwood, 1992). Conodonts from a limestone clast in the Grizzly Formation are the same genera as those in the underlying Sierra City mélange of the Shoo Fly Complex, supporting the idea that detritus in this part of the unit was sourced from the underlying rocks. The overlying Sierra Buttes Formation (which includes the Elwell Formation of Durrell and D’Allura, 1977) near Taylorsville has yielded Frasnian to Famennian (Late Devonian) radiolarians from chert low in the section, with similar radiolarians along with middle Famennian ammonites higher in the section near Gold Lake and Bowman Lake (Harwood, 1992). The Taylor Formation lacks internal age control, but the age is tightly constrained by the age of the units above and below. It is conformably overlain by the volcanic lower member of the Peale Formation, which has yielded late Kinderhookian (middle Tournasian, middle Early Mississippian) conodonts from limestone lenses in tuff south of Genesee and near Frazier Falls (Harwood, 1992). The upper chert member, which gradationally overlies the volcanic member locally, has yielded radiolarian assemblages that range from late Osagean (early Visean, early Middle Mississippian) to Desmoinesian (early Moscovian, early Middle Pennsylvanian) throughout the outcrop area of the unit from the northernmost block east of Lake Almanor to the southernmost block west of Big Valley (Harwood, 1992).
West of Lake Tahoe this unit also includes the lower part of Lake Tahoe sequence of Harwood (1988). The Picayune Valley Formation at the base of the unit has yielded only echinoderm fragments suggestive of a Late Silurian to Late Devonian age (Harwood, 1992). This formation is mapped as unconformably overlying the Shoo Fly Complex, and on Five Lakes Creek as interfingering with and overlying the Late Devonian Sierra Buttes Formation (Harwood and others, 2014), so it must be Late Devonian as well. The Picayune Valley Formation is gradationally overlain by the Serena Creek Formation. No fossils have been found in the Serena Creek Formation, but it may correlate with the chert member of the Early Mississippian to Early Pennsylvanian Peale Formation (Harwood and others, 2014). The Serena Creek Formation is gradationally overlain by the Onion Creek Formation. Quartzite near the base of the Onion Creek Formation has yielded a bivalve shell fragment suggestive of a nucleospirid brachiopod, which ranges in age from Late Silurian to Mississippian. If the fossil is indeed a nucleospirid, that would mean the age of the Onion Creek Formation would be Mississippian, given the age and correlation of underlying units.
Devonian volcanic members of this unit are coeval with, and intrusively linked to, the Devonian part of the Sierra Buttes intrusive suite (unit Gsb), together comprising the Sierra Buttes arc. The Sierra Buttes Formation is locally cut by hypabyssal intrusions, mainly basaltic andesite to rhyolite and exhibit evidence of interaction with wet, unconsolidated sediments beneath the seafloor (Hanson and others, 1996).