GENU UAL DISTRIBUTION OF THE GRAVELS. 



303 



'. 



yet Calaveras is prolific in quartz veins, some of which have been quite pro- 

 ductive, although not usually holding out well in depth. But little progress 

 was made in this county towards tracing out the connection of the channels. 

 The most continuous one seems to have been that descending from the High 

 Sierra in the vicinity of the Mokelumne River, and so extensively worked 

 "in the early days" at Mokelumne City and afterwards near Chili Gulch. 

 The channel was narrow and the gravel was thin, but exceedingly rich in 



places* In Amador, the next county north of Calaveras, the association of 

 gravels with volcanic materials becomes more and more a feature of the 

 geology,! although the detrital masses have not yet attained anything like 

 the importance which they have farther north. The quartz veins of Amador, 

 belonging mostly to the system of the "Mother Lode," are large; and, 

 although not as rich as in some other places, have been worked to greater 

 depth, more continuously, and with perhaps larger profits in the long run, 

 than anywhere else in the State. 



The region drained by the different branches of the American River is one 

 in which all the peculiar features of the gravel-mining portion of the Sierra 

 are well displayed. From the neighborhood of Placerville north to the North 

 Pork of the American, the central belt of the range, between the altitudes of 

 2,500 and 5,500 feet, is largely covered with volcanic materials; and between 

 the Middle Fork of the Middle Fork and the North Fork all the higher por- 

 tions of the divides are flat tables of lava, deeply cut into by erosive action, 

 so as to leave many disconnected patches of this material, as will be noticed 

 on the maps given in a previous chapter of this volume,} The total thick- 

 ness of the detrital and volcanic formations lying on the bed-rock is, in portions 

 of the region in question, very large, quite often reaching 400 or 500 feet, 

 and occasionally much exceeding that. The larger part of this thickness, 

 however, is made up of various forms of lava, the gravel proper rarely 

 reaching as much as 100 feet. The heavier deposits of the latter lie, 

 usually pretty well down on the range, say at an altitude of from 2,500 to 

 3,500 feet. But a small portion of the gravel in this region has been un- 

 covered by the erosion of the overlying volcanic materials, and an inspection 

 of the maps referred to above will show how patches of it occur, in some 

 places almost continuously along the edges of the lava, their position indi- 

 cating how large a part of the non-volcanic sedimentary deposits must yet 

 remain covered. 



* See ante, p. 128. 



t See ante, p. 102. 



4- 



See Plates B and C, opposite pages 82 and 98. 



