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The northwest trending (N45°W) batholith is the dominant feature in the Whiskeytown area. This dominance of the local topographic expression is due to its preferential resistance to erosion in contrast to the surrounding country rock. Its total exposed length is about 48 km (30 miles) and its widest point is about 14 km (9 miles). There are several satellite plutons, identical in composition that crop out around Shasta Bally. One of the largest, the Clear Creek plug, covers more than 2.5 square kilometers (1 square mile). Contacts between the batholith and the surrounding, foliated, gneissic country rocks, are sharp.
The Shasta Bally batholith is an igneous pluton, which intruded the older assemblage of quartz-mica schists, felsic and mafic volcanic rocks, conglomeratic and shaly sedimentary rocks ranging in age from the Precambrian to the Mississippian (Albers, 1965; Irwin, 1999). This intrusive event occurred during the Late Jurassic- Early Cretaceous and was contemporaneous with the Nevadan orogenic event. During this time, plutonism was also occurring in the area that became the Sierra Nevada mountains, southeast of Whiskeytown.
1848 Historical Structures
Though Whiskeytown National Recreation Area was set aside to preserve a natural area for outdoor activities focusing on the reservoir, careful attention must be paid to the historical context found in the area as well. This context is centered on the geologic resources of the area, which attracted early mining interest and settlement. The preservation and restoration of the historical features present at Whiskeytown will add to the heritage of the gold rush story for this and future generations.
When the considerable placer deposits in the Whiskeytown area were exhausted, attention moved toward mining the hillsides for lode gold in massive sulfide deposits and gold- bearing quartz veins. Mining in the area has been active intermittently since 1848 with extraction of copper, zinc, pyrite, gold, and silver (Albers, 1964).
In the quest for gold and other heavy metal deposits of the French Gulch area, more than 40 mines were excavated. Whiskeytown National Recreation Area is located in the Whiskeytown mining district. This district is one of 4 in the area which include the French Gulch- Deadwood, Muletown, and South Fork districts. The mines in the Whiskeytown district include the Eldorado, Gambrinus, Ganim gold- talc, Mad Mule, Mad Ox, Mount Shasta, and Truscott mines. Production of gold from the district is estimated between 68,700 and 71,500 ounces of gold.
The geology associated with the different deposits varies. Contacts between the Bragdon Formation (described below) and intrusive igneous rocks are host to the Mad Mule and Truscott mines. Northwest- trending structures in the Balaklala Rhyolite and Copley Greenstone are the focus of the Mount Shasta and Ganim mines. Veins trending east- west in the Mule Mountain comprise the Mascot, Eiller, and numerous other small deposits (Albers 1965).Veins in the Copley and Balaklala Formations as well as the Mule Mountain stock were much less productive in terms of gold recovered than in the Bragdon Formation contacts more prevalent in other districts.
The Reservoir and Whiskeytown Dam
The dam is located in the Clear Creek drainage basin about 18 km (11 miles) west of the junction with the Sacramento River Valley in the southeastern portion of the Klamath Mountains physiographic province. The basin is bordered on the east by the, relatively low elevation (701 m [2,300 ft])Mule Mountain range. The higher peaks of the Shasta Bally mountains, which grade northward into the Trinity Mountains form the western boundary. The Trinity Mountains separate the Clear Creek drainage from the Trinity River drainage (BOR, 1995). The drainage area for the reservoir is 524.5 square kilometers (202.5 square miles).
The crest elevation of the dam is 374 m (1,228 ft) with the structural height of the dam at 86 m (282 ft). The dam and its associated dikes are composed of zoned earthfill, a mix of rocks, sand, boulders, mud, etc. The dam is constructed on the Balaklala Metarhyolite Formation and the granite of the Mule Mountain Stock.
The reservoir behind Whiskeytown Dam, Whiskeytown Lake, is a major northern California recreation attraction (figure 9). The lake provides 58 km (36 miles) of shoreline and 3,200 surface acres of water. The normal surface elevation of the reservoir is 369 m (1,210 ft) with a hydraulic height of 77 m (252 ft). The dam is not gated. However, the Judge Francis Carr Powerplant on the west end of the lake generates power. The powerplant has two generators with a total capacity of 154,400 kilowatts and has been in service since May, 1963 (BOR, 2003).
The contact between the sedimentary rocks of the Mississippian Bragdon Formation (a primary gold producer) and the underlying igneous intrusives is thought to be a low- angle thrust fault. In areas where contacts are exposed, the Bragdon is highly deformed, faulted, and intruded. Intrusive igneous activity focused along the faulted areas (Albers, 1965). Magma favors preexisting fractures and weaknesses in a rock.
There are numerous faults running through the park, although many are difficult to locate due to the poor exposures and a lack of stratigraphic markers necessary to determine clear offset in the igneous rocks. Most appear to trend northwest to southeast, with secondary faulting trending northeast to southwest. The majority of these faults have little inferred offset.
The Hoadley Fault virtually bisects the park from the northwest end to the southeast corner. It is a normal fault with the downthrown side to the northeast that generally dips 50º- 65º to the northeast. Movement along this fault likely occurred around 140 Ma.
Faults, linear ultramafic bodies, or granite plutons separate these tectonostratigraphic lithic belts, which contain both volcanic and sedimentary units with associated deep- seated intrusive granites, and nearsurface intrusive rocks of Devonian through Cretaceous age (Irwin, 1966). By the early Cretaceous, after at least 8 different major accretionary events, belts of sutured terranes comprised the southern Klamath Mountains. From east to west, these terranes are called: 1) eastern (Paleozoic) Klamath belt (Redding, Trinity, and Yreka subterranes ~399- 380 Ma), 2) central metamorphic terrane (~220 Ma) – Fort Jones terrane (~198- 193 Ma), 3) North Fork terrane (~180 Ma), 4) Eastern Hayfork terrane (~168 Ma), 5) Western Hayfork terrane (~164 Ma), and 6) Rattlesnake Creek terrane (~150 Ma) (figure 10) (Irwin, 1966; 1999). The granites and near- surfaceintrusives form another series of interstitial belts comprised of bodies of equivalent age that are divided into pre- and post- amalgamation referring to the timing of their emplacement relative to the addition of the major tectonostratigraphic belts. The interstitial belts vary on the degree of metamorphism from unmetamorphosed to amphibolite facies (Danielson and Silberman, 1987).
The eastern Klamath belt is comprised of an essentially homoclinal sequence of layers dipping to the east and terminating with some deformation against ultramafic intrusive rocks. In aggregate the sediments are 12,000 to 15,000 m (40,000 to 50,000 ft) thick and range in age from Ordovician to Jurassic, although the Ordovician and Silurian rocks are limited to exposures in an isolated northernmost part of the belt.
The central metamorphic terrane consists mainly of the Abrams mica schist and the Salmon hornblende schist. It is separated from the eastern Klamath belt by ultramafic igneous rocks and from the western Paleozoic and Triassic belt by faulting with no associate intrusives (Irwin, 1966). The Abrams mica schist is a composite unit which includes metasedimentary rocks occurring both above (Grouse Ridge Formation) and below (Stuart Fork Formation) the Salmon hornblende schist.
The lower rocks are considered fensters in a regional thrust plate formed by Salmon hornblende schist and theGrouse Ridge Formation. The metamorphic history of the area is complex. The regional grade generally ranges from upper greenschist to almandine (garnet)- amphibolite facies with some retrograde metamorphism as well (Davis, 1966).
The terranes west of the central metamorphic terrane consist of phyllitic detrital rocks, radiolarian (fossils) chert, mafic volcanics, and crystalline limestone, which have been intruded by ultramafic and granitic rocks. The grade of metamorphism ranges from low- grade greenschist facies to amphibolite facies. Some fossils have been identified from this belt including Late Pennsylvanian or Early Permian fusulinids and Permian and Triassic ammonites (Irwin, 1966).
The westernmost belts are composed mainly of the Galice Formation and the South Fork Mountain schist. The Galice Formation, dated as Late Jurassic, is composed of a lower metavolcanic unit and an upper metasedimentary unit. The metavolcanic unit is composed mainly of meta- andesite flows and breccias and may be over 2,100 m (7,000 ft) thick. The upper unit is mostly slaty mudstone and foliated greywacke. The South Fork Mountain schist is well- foliated quartz-mica schist extending in a narrow north- south band along western boundary of the Klamath Mountains for about 242 km (150 miles) (Irwin, 1966).
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