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Collection: Directories and Documents
Mineral Land Classification of Nevada County, California (1990) (235 pages)
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Page: of 235
overlying the Sailor Canyon Formation is the Middle Jurassic
Tuttle Lake Formation, which is composed predominantly of mafic
to andesitic volcanic flow and breccia deposits.
CENTRAL METAMORPHIC TERRANE:
The Central metamorphic terrane is bounded on the west by
the Gillis Hill fault and by a series of unnamed and poorly
defined thrust faults extending through Scotts Valley Reservoir.
On the east, the Central metamorphic terrane is bounded by the
northern Melones fault (Figure 3; Plates la and 1b). Rocks
within the Central metamorphic terrane are assigned to the
Permian and Triassic Calaveras Complex and to the Triassic
Clipper Gap Formation.
Calaveras Complex: Principal rock types making up the
Calaveras Complex include moderately metamorphosed chert,
argillite, volcanic, and volcanic-derived sediments that were
probably deposited in a marginal ocean basin environment in
proximity of volcanic activity. Parts of the formation have been
highly disrupted into a serpentinite-matrix melange.
Clipper Gap Formation: The Clipper Gap Formation consists
of a weakly metamorphosed, but highly disrupted assemblage
(melange) of metasedimentary rocks of probable Triassic age
(Tuminas, 1983). The principal rock types are chert and
argillite which were deposited in a deep ocean basin environment.
Also included in the unit are a few isolated carbonate rock
bodies. In the southern part of the county, the Clipper Gap
Formation underlies volcanic rocks of the Western metamorphic
terrane and are exposed in several areas as windows (Plate la).
WESTERN METAMORPHIC TERRANE:
The Western metamorphic terrane encompasses most of the area
of Nevada County east of the Gillis Hill fault (Figure 3; Plate
la). Predominant rock types in this terrane are igneous and
sedimentary rocks of island-arce origin. The terrane is marked by
several regional high-angle faults and a number of low-angle
(thrust) faults that juxtapose distinct lithologic assemblages of
Mesozoic age. These assemblages have been mapped, described, and
named by previous workers as follows:
Smartville Complex: The part of the western metamorphic
terrane that is situated between the county line and the Wolf
Creek fault consists almost entirely of mafic to intermediate
volcanic, hypabyssal, and plutonic rocks which were formed along
the magmatic core of an island-arce chain active during the
Jurassic. This assemblage of rocks has been referred to as the
Smartville Complex (Beard, 1985).