GEOLOGIC MAPS AND NOTES ALONG HIGHWAY 49 BOWEN AND CRIPPEN 



77 



narrow belt of serpentine and related basic intrusive rocks which are not 

 particularly well exposed along the highway except in deeply weathered 

 readouts. Deeply weathered areas and dark-red soil mark remnants of 

 the old Eocene surface. The remainder of the route into North San Juan 

 lies on a granitic bedrock ranging in composition from quartz diorite to 

 granodiorite. A small roof pendant or remnant of overlying wall rock 

 of dark green amphibolite can be seen in readouts 1.2 miles south of the 

 Yuba River bridge. The greenstone is cut by aplite and pegmatite dikes. 

 A good locality for collecting hornblende crystals is to be seen close to 

 the amphibolite contact. 



Close to the south abutment of the Yuba River bridge, a broad road- 

 cut and quarry in granodiorite afford an excellent close-up view of the 

 intruding batholith. The coarse matrix is full of large inclusions or 

 enclaves and several prominent joint systems prevail which have aided 

 in quarrying the rock for fill. The scenic gorge of the South Fork of the 

 Yuba is well worth seeing. The river water is often discolored by tailings 

 from hydraulic workings upstream. 



The road cuts up the grade along the north wall of the Yuba River 

 canyon expose granitic rocks of at least two separate intrusive bodies. 

 Contacts between the intrusions are indistinct, granodiorite grading into 

 darker hornblende diorite which is cut by light-colored dikes of variable 

 texture. 



In the vicinity of Shady Creek bridge extensive deposits of Quater- 

 nary gravels choke the river bed. These are partly the result of placer 

 operations connected with Tertiary gravels situated upstream. 



One mile northwest of Shady Creek bridge an unpaved road inter- 

 sects Highway 49 which connects with the hydraulic mines of Cherokee, 

 North Columbia, North Bloomfield, Relief, Omega and many others. The 

 Cherokee diggings are six miles northeast of the above intersection, 

 North Columbia is a little over nine miles, and North Bloomfield is about 

 19 miles. The immensity of the North Bloomfield pits must be seen to be 

 believed. Although excavated entirely by powerful jets of water, the 

 pits compare favorably in size with many of the open pit copper and iron 

 mines of other states which have been excavated by modern mechanical 

 means. The Malakoff pit west of North Bloomfield resembles a miniature 

 Bryce Canyon. The soft clay and gravel walls have been fluted and other- 

 wise sculptured by erosion into ' ' badlands ' ' of great charm. The pastel- 

 colored horizons in the pit gravels contrast strikingly with the deep red 

 soil mantle and the dark-green backdrop of forest trees. Some idea of 

 the achievement of the nineteenth-century hydraulic miners in moving 

 such great quantities of material without modern equipment may be had 

 from the following figures : 20,000,000 cu. yds. were excavated at North 

 Bloomfield ; and 25,000,000 cu.yds. from North Columbia. Only 14 percent 

 of the gravel reserves at North Columbia had been removed by the time 

 hydraulic mining was stopped by court injunction in 1884. The problem 



of the debris from such operations was, of course, a great one. It choked 

 the rivers below and ruined riverbottom lands for farming purposes. 

 In some places the problem has been solved by building debris dams ; in 

 others by selective spreading of waste on already valueless areas. A few 

 hydraulic mines such as Relief and Omega situated southeast of North 

 Bloomfield are currently in operation, -but most have been idle since 

 the 1 880 's. 



Petersons Corner, 1.2 miles northwest of the North Columbia-High- 

 way 49 intersection is the terminus of a paved road connecting with the 

 hydraulic-mining towns of Sweetland, Birchville, French Corral, and 

 Bridgeport. An interesting and a scenic sidetrip on this road will bring 

 one out on Highway 20 at Bitney Corner a few miles west of Nevada 

 City. The route lies principally through granitic basement rocks which 

 have been deeply weathered into a lateritic red clay in many places. An 

 occasional belt of black or green meta-volcanics may be seen bordered on 

 either side by granitic rocks. The many Tertiary gravel deposits lying 

 on this surface are the basis for the once thriving hydraulic mines. 



Sweetland, of which Petersons Corner is a part, was originally a 

 placer-mining camp first settled in the early 1850 's. Together with adjoin- 

 ing towns to the southwest, Sweetland was a going and prosperous town 

 until the ban on hydraulicking took away the principal source of income 

 of the region. Sweetland is now a handful of frame dwellings set in a 

 quiet country landscape. Birchville, 1.5 miles southwest of Sweetland, is 

 located principally by the hydraulic pits to the north of the old town site. 

 Several are filled with water and form small lakes. 



Three miles below Birchville is French Corral which dates from 1849. 

 The town is located in an attractive valley on a tributary to the South 

 Fork of the Yuba River. Several well preserved stone and brick buildings 

 remain along the main street. French Corral was at one end of the first 

 long distance telephone line ever built. It connected with Birchville, 

 Sweetland, North San Juan, Cherokee, North Columbia, North Bloom- 

 field and Bowman or French Lake, a distance of 58 miles. 



Very little remains at the Yuba River site of Bridgeport, three miles 

 southwest of French Corral. A covered wooden bridge spans the river and 

 red ranch buildings remain inside stone-walled corrals. A partly over- 

 grown graveyard is located beside the road a short distance south of the 

 river. There is little of particular geologic or historical interest between 

 Bridgeport and Bitney Corner on Highway 20, but the landscape is an 

 attractive one and the side route will draw travelers who like to keep off 

 the beaten track. 



North along Highway 49 from Petersons Corner, remnants of the 

 exhumed Eocene surface are evident in several places. This flat surface 

 is particularly noticeable in the vicinity of North San Juan. Large 

 hydraulic diggings can be seen to the west. The granitic basement rocks 

 are a dark or melanistic phase of the ordinarily light-colored granodio- 

 rite, being rich in biotite mica. 



