58 



GEOLOGIC GUIDEBOOK ALONG HIGHWAY 49 



[Bull. 141 



look upward 1000 feet higher to the two stubs of the severed Table 

 Mountain latite. On the north side may be seen high up on the canyon 

 wall the V-shaped cross-section of the lava-filled channel, cut in granitic 

 rock. Before the uptilting of the Sierra Nevada, this lava occupying the 

 sinuous course of what may have been the ancestral Stanislaus River, 

 flowed across this place, then at a much lower elevation. As the Sierra 

 Nevada block was raised and tilted slightly westward, the present newly 

 born Stanislaus River, flowing down the Sierran slope cut and carved 

 a canyoja through the lava and underlying rocks, keeping its course as 

 the Sierran surface rose, and cutting deeply into the granite. Not only 

 is this lava-filled channel cut in two, but also the earlier Columbia 

 channel is bisected. A continuation of this channel which was left just 

 north of Columbia is again encountered on the road as it reaches the old 

 surface after the climb out of the canyon. The road follows along this 

 ancient channel and the edge of the present Coyote Creek canyon at the 

 bottom of which, 300 feet lower in elevation, is a Natural Bridge or 

 remnant of a limestone cave through which the creek now flows. 



Moaning Cave, a limestone cavern privately owned but open to the 

 public, is located on the opposite side of Coyote Creek canyon and may 

 be seen from the road. It is also two miles from the junction in Vallecito. 



As one travels west into Angels on Highway 4. the head frames of 

 the Golden River, Vallecito Western, and Slab Ranch mines are seen to 

 the north of Highway 4. These drift mines are now all idle and filled 

 with water. Though the geology of the Tertiary channels is not very well 

 known, it is possible that this Central Hill Channel may be part of the 

 same stream system as the Columbia River Channel which was bisected 

 by the Stanislaus River. 



Two-tenths of a mile from the junction of Highways 4 and 49 in 

 Angels Camp the site of the old chlorination plant is located. Chlori- 

 nation was an early day method for recovering gold from concentrates 

 before the process of cyanidation was discovered. 



Two mining districts of considerable interest lie to the west of Alta- 

 ville along Highway 4. Dumps and prospect holes of the Gold Hill pocket 

 mining district can be seen a short distance to the north of the road. The 

 Wagon Rut mine was the best known of the Gold Hill mines. The head- 

 frame of the Belmont-Osborne mine is situated half a mile southwest of 

 the Gold Hill group and can also be seen from the road. 



Several interesting sidelights on the wildlife of the vicinity may be 

 observed along the Copperopolis route. Telephone poles and fence posts 

 are riddled by the acorn studded holes of California woodpeckers. The 

 fence posts are further burdened by the carcasses of dozens of predatory 

 animals which the ranchers have trapped or otherwise disposed of. It 

 seems to be a custom of the country to exhibit" varmints "in this fashion. 

 No less than 34 coyotes and three bobcats were strung on consecutive 



fence posts within a two-mile stretch on the authors' last trip through 

 that country ! 



The Copperopolis copper mining district 12 miles southwest of Alta- 

 ville was a major producer through both World Wars but has been idle 

 much of the time between war periods. The North Keystone, Empire, and 

 Keystone-Union are the principal mines of the district and are all located 

 in town within a short distance of each other. The Copperopolis mines 

 were discovered in 1861 and for several years thereafter were the prin- 

 cipal producers of California copper. The upper parts of the ore bodies 

 were very rich and the Union and Keystone mines paid huge dividends. 

 The Copperopolis mines are on a fault system as are the Mother Lode gold 

 mines, but the Copperopolis mines carry little gold and lack the quartz- 

 carbonate gangue of the Mother Lode veins. The ore is of simple sulfide 

 type, principally pyrite and chalcopyrite and is exceptionally free of base 

 metallic elements other than copper. The massive sulfides pass into 

 pyritic or chalcopyritic slate at peripheries of the ore shoots. The ore 

 bodies lie in a narrow belt of hydrothermally-altered black slate of the 

 Mariposa formation with Logtown Ridge meta-andesite agglomerate on 

 either side. Dikes of diorite cut the Logtown Ridge in many places near 

 Copperopolis paralleling the strike of the bedded rocks. 



The town of Copperopolis, located in the center of Salt Springs 

 Valley, has but few buildings remaining. The red brick I.O.O.F. Hall, 

 originally built in 1862 as a church, is one of the few still in a good state 

 of preservation. A Mr. McCarty had mined and farmed in Salt Springs 

 Valley as early as 1852 and had prospected the copper veins for gold. 

 Finding no gold, he paid no further attention to the copper deposits 

 until he returned with two others in 1861 and helped to found Copper- 

 opolis. The history of Copperopolis has been one of periods of great 

 activity interspersed with periods of virtual abandonment. The copper 

 district is currently idle because of high operating costs. 



North from Altaville there is little of geologic interest along the 

 highway until Calaveritas Creek is reached. The gently rolling grazing 

 land is probably much like the ancestral Eocene land surface. Remnants 

 of auriferous gravels can be seen to the east of the road particularly 

 between Calaveritas Creek and San Andreas. The bedrock is schist and 

 greenstone of the Calaveras formation. In several places along Calaveritas 

 Creek, both southeast and southwest of San Andreas, limestone lenses 

 occur in the Calaveras which are suitable for use in making Portland 

 cement. Although parts of the lenses are dolomitic and carry too high a 

 magnesia content for cement, excellent bodies of cement-grade limestone 

 occur in them and are being exploited at the present time. The Calaveras 

 Cement Company has a large plant situated a short distance west of 

 Highway 49, 2 miles south of San Andreas. The company allows visitors 

 at its plant which is well worth going through. Historic Kentucky House 



