Gold 



317 



to construct tunnels into the buried gravels in quest of the 

 buried treasure of secondary gold. 



The following is from Julihn & Horton, Bull. 424, U. S. 

 Bureau of Mines: "Nowhere in the world has so much gold been 

 taken from so small an area of placer ground as in the Columbia 

 Basin of Tuolumne County. There on an open flat within a 

 radius of a single mile $5 5,000,000 in nuggets and gold dust was 



Photo by G. K. Gilbert, U. S. Geol. Survey 



FIG. 93. Limestone, at Columbia, Tuolumne County. The limestone 

 was sculptured by erosion, later buried by gold-bearing earth washed from 

 higher lands, then exposed by placer mining. 



panned, rocked, or sluiced by miners from 1853 to 1870. To- 

 day there is no active mining within the basin, where only the 

 white pinnacles of the deeply eroded limestone bedrock serve 

 as monuments to the once thriving placer industry. 



"This richest of the world's known placers resulted from a 

 fortunate combination of geologic causes. Natural riffles of 

 irregularly eroded white, crystalline limestone bedrock about 



