GEOLOGIC MAPS AND NOTES ALONG HIGHWAY 49 BOWEN AND CRIPPEN 



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is located near by. The plant can be reached by two different roads 

 connecting with Highway 49 close to San Andreas. A private road and 

 overpass which connects the plant to its eastern limestone quarries crosses 

 Highway 49 at the Calaveritas Creek bridge. 



San Andreas, as the name implies, was first settled by Spanish Cali- 

 fornian miners prior to the advent of the Yankee. As usual they were 

 persecuted and driven out of town whereas other minority groups such 

 as the Chinese were allowed to remain. Present day San Andreas is an 

 attractive town, more or less typical of the Mother Lode, and full of old 

 buildings dating from as early as 1851. Division of Highways Historical 

 Marker 222 stands at the corner of Highways 49 and 12. Highway 12 con- 

 nects with the old towns of Railroad Flat and Westpoint to the northeast 

 of San Andreas. As county seat of Calaveras County, San Andreas 

 boasts both the County Courthouse and County Museum. The museum 

 occupies one of the best preserved, oldest buildings in town and contains 

 rocks, minerals, artifacts, Indian handcraft, and miscellaneous objects 

 and manuscripts of historical interest. 



Proceeding northward from San Andreas, Highway 49 traverses four 

 miles of rolling grazing land of no particular geologic interest. The head- 

 frame and buildings of the Kate Hageman mine are located near the 

 bridge which crosses the North Fork of the Calaveras River, 2.2 miles 

 northwest of San Andreas. The Kate Ilageman was developed during the 

 1930 's and considerable modern mill equipment was installed. Both 

 opencut and underground mining has been attempted there. The mine 

 has been idle for some time. Wall rocks are greenstone and slate; a 

 serpentine contact is close by to the west. The creek bottoms near the 

 Kate Ilageman have been worked for placer gold. 



Two miles northwest of the Kate Hageman mine, a rather extensive 

 group of Tertiary deposits is exposed on both sides of the highway from 

 the vicinity of Chili Gulch to Mokelumne Hill. The ancient Mokelumne 

 Hill river channel once traversed this region in a southwesterly direction 

 and was joined, in the Chili Gulch vicinity, by a tributary which entered 

 from the direction of San Andreas. Remnants of the old channel gravels 

 have been extensively worked for gold by hydraulic and other placer 

 means. The lofty faces of the hydraulic pits are not visible from Highway 

 49 but some of the gravels are exposed in road cuts east of Chili Gulch. 

 The gravels lie nonconformably on schists and greenstones of the Cala- 

 veras formation and are overlain by the rhyolite tuff of the Valley Springs 

 formation and the andesite and andesite gravels of the Mehrten formation 

 in that order. Unconformities exist between the Valley Springs and 

 Mehrten and even within the Mehrten itself. The Valley Springs is 

 probably Miocene and the Mehrten is probably Pliocene at least in part. 

 Cliffecl outcrops of yellowish-gray tuff of the Valley Springs forma- 

 tion are prominent in many places along the Mokelumne grade. Expo- 

 sures of the Mehrten can best be seen a short distance west of the town of 



Mokelumne Hill along Highway 8. A quarter of a mile south of the 

 Calaveras Crystal mine, the Calaveras bedrock has been intruded by 

 diorite. Dioritic rocks form the basement on which the Tertiary rests 

 over a large area in the vicinity of Mokelumne Hill. 



The Calaveras Crystal is a drift mine driven beneath the Valley 

 Springs rhyolite opposite the Chile Creek placer diggings. It can be 

 reached via dirt road from Highway 49, the road joining Highway 49 

 from the east at a point 6.5 miles from San Andreas or 2.5 miles from 

 Mokelumne Hill. The mine is on a branch of the Mokelumne Hill channel 

 system known as the Tunnel Hill channel. The large quartz crystals which 

 have made the mine famous are partly of optical and electronic grade. 

 Considerable quartz for this purpose was marketed during the recent war 

 emergency. Crystals weighing as much as 100 pounds each have been 

 taken from the Calaveras Crystal. An adjoining mine on the McSorley 

 Ranch operated by the Rough Diamond Mining Company also produced 

 considerable quantities of optical-grade quartz. Although not so well 

 known as the Calaveras Crystal, reserves of quartz crystals in this mine 

 appear to be greater than those of its more famous neighbor. 



Mokelumne Hill was founded in 1848 by ex-members of Stevensons 

 Regiment of Mexican war fame. A stone historical monument erected by 

 the Native Daughters of the Golden West is located close to the three 

 story I.O.O.F. building. The latter building was erected in 1854 and 

 added to in 1861 and is the first three story building in the Mother Lode 

 country. Mokelumne Hill and Jackson once engaged in a feud over the 

 problem of which town should get the honor of being county seat. Origi- 

 nally, Double Springs, some miles to the west of Mokelumne Hill, had 

 acted as county seat until rapidly growing Mokelumne Hill claimed the 

 honor. Jackson finally ' ' seceded ' ' from Calaveras County and formed a 

 county and county seat all its own, now Amador County. The present 

 Amador-Calaveras County line follows the course of the Mokelumne 

 River in this area. San Andreas is now the county seat of Calaveras 

 County. Highways 5 and 8 cross 49 at Mokelumne Hill, Highway 8 con- 

 tinuing on to the east to mining districts in the vicinity of Westpoint. 



Near the junction of Highways 8 and 49, a group of underground 

 rooms and quarries, from which rhyolite tuff building stone was taken, 

 can be observed. Mokelumne Hill was fortunate in having so satisfactory 

 a source of building material so close at hand. 



Readouts to the west of Mokelumne Hill along Highway 8 afforded 

 closeup views of the late Tertiary volcanic sequence. Three miles from 

 the junction of 8 and 49, a long cut exposes the trace of a low-angle thrust 

 fault which cuts both the schist bedrock and the overlying Mehrten rocks. 

 This is an unusual type of post-Pliocene faulting for this area, although 

 the fault is probably not of major extent. The trace of this same fault 

 can be seen in the undercut face of one of the volcanic plugs to be seen 

 on the south side of the road three-tenths of a mile farther west. This 



