32 



GEOLOGIC GUIDEBOOK ALONG HIGHWAY 49 



[Bull. 141 



Canvas hose was soon replaced by iron pipe. Special heavy iron or steel 

 spouts and nozzles, such as the Monitor, Giant or Dictator were invented 

 and put in use. Their modern versions have double joints to give hori- 

 zontal and vertical movement, and deflectors to utilize the reactive force 

 of the water to permit easy turning. The largest sizes, under a head of 

 400 feet will handle a flow of over 4500 cubic feet of water a minute. 

 In ordinary practice, however, in California, in 1867, a flow of 500 miner's 

 inches (about 750 cubic feet per minute) was considered a satisfactory 

 amount. This was increased with the opening of large mines with banks 

 several hundred feet high, and the use of 1000 to 1500 miner's inches 

 of water per giant became common, with heads as high as 450 feet. The 

 water was often assisted by ' ' bank blasting ' ', where T-shaped adits were 

 run into the gravel bank, or a shaft with short drifts at the bottom was 

 sunk, the arms of the T being loaded with several thousand pounds of 

 black powder or low-strength dynamite which was fired to break down 

 the bank. Long tunnels also had to be run in many cases to give drainage 

 through the rim of the old channel. In spite of these heavy expenses, 

 hydraulic mining was cheap, and permitted working large bodies of 

 gravel at a profit even when their gold content was 10 cents a cubic 

 vard or less. 



T'IC. 1. A view of the Mother Lode in Ammlor County showing the Runker Hill 

 mine in foreground, the Treasure mine in the center, and the headframe of Fremont 

 mine in the left background. 



Drift Mining 



Although the mining of buried ancient river channels by means of 

 shafts and adits was started very soon after the outcrops of gravel were 

 noticed on the hillsides, and at about the same time as hydraulic mining, 

 it has not suffered from the restrictions laid upon hydraulicking. The 

 hundreds of miles of such channels, the oldest of which were flowing 

 streams as early as Cretaceous time on what is now the western slope 

 of the Sierra Nevada, were buried and preserved under volcanic mud 

 and coarser rock ejected by eruptions in the higher Sierra Nevada. The 

 ideal method of mining these channels is to determine if possible the 

 lowest available point in the trough of the channel and to open it by 

 running an adit from an outlet or through one rim to give drainage 

 and permit following the channel upstream, with the adit either on the 

 bedrock or in bedrock far enough below the gravel to give a solid roof, 

 through which raises are put up and working faces opened across the 

 payable width of gravel. Some channels have been followed and mined 

 for several miles. The Forest Hill Divide in Placer County was the most 

 celebrated of the drift mining districts. The mining method resembles 

 that used in coal mining. Much of the gravel was found to be cemented 

 and had to be milled or washed several times after lying in the open 

 air to aid disintegration. Stamp mills with coarse screens were found 

 to be most suitable for milling cemented gravel. 



Dredging 



The pioneers made a number of abortive attempts to dredge gold 

 from the river beds. In 1897, gold dredging with a single-lift elevator 

 type of bucket dredge was attempted on Yuba River, but the first suc- 

 cessful operation was started in March 1898 at Oroville by \V. P. Hammon 

 and Thomas Couch. This dredge had open-link buckets of three cubic 

 feet capacity and a tailing stacker. Close-connected buckets, belt con- 

 veyor stackers for tailing, and electric power were introduced in 1901. 

 On the American River near Folsom, dredging was started early in 1899 

 by Colorado Pacific Gold Dredging Company. These earliest dredges 

 used steam for power and worked 30,000 to 35,000 cubic yards of gravel 

 a month. The American genius for large scale operation can be seen in 

 the steady increase in yardage and depth capacity. W. P. Hammon and 

 R. D. Evans started in the Yuba River field in 1903 with a dredge having 

 Buckets of six cubic feet capacity and a shaking screen. It could dig 60 

 feet below water level. Revolving screens appear to have become standard 

 in 1905. Since then, this type of dredge has been put on practically every 

 gold-bearing river in northern California, but the most important fields 

 have been Yuba River near Hammonton, American River near Folsom, 

 and Feather River near Oroville. Gold production of over $100,000,000 

 from Yuba County, over $95,000,000 from Sacramento County and 

 about $60,000,000 from Butte County since dredging started has been 



