ABSTRACTS 



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GEOLOGY. — Hydraulic-mining debris in the Sierra Nevada. Grove 

 Karl Gilbert. U. S. Geological Survey Professional Paper 105. 

 Pp. 154, with maps, sections, and illustrations. 1917. 



Historical outline is given of the development of hydraulic mining 

 in the Sierra Nevada, the encroachment of its tailings on valley lands, 

 its subsequent restriction and regulation, and the circumstances lead- 

 ing to a study of the subject by the Geological Survey. 



The tailings from hydraulic mines were in part deposited on neigh- 

 boring slopes and in neighboring stream valleys and canyons and in 

 part delivered to rivers that carried them forward. At the base of the 

 range were large deposits on the piedmont slopes and other deposits in 

 the beds of valley rivers. As a consequence of the piedmont and river- 

 bed deposits rivers rose higher in time of flood and lands previously 

 immune were inundated. The reclamation of basin lands and delta 

 lands for agriculture by surrounding them with levees also aggravated 

 flood conditions, and the results of the two causes were inseparable. 



Comparison of maps of early and late dates shows that large deposits 

 have shoaled the bays of the San Francisco system, and reduced their 

 areas. These deposits, ascribed to hydraulic mining and to the in- 

 crease of soil waste by agriculture and other industries, since the dis- 

 covery of gold have amounted to more than 1100 million cubic yards. 



The sand brought to the head of Suisun Bay by Sacramento and San 

 Joaquin rivers is swept onward in the bays by tidal currents but is not 

 believed to reach the Golden Gate bar in any appreciable quantity. 



The stress that caused the restriction of hydraulic mining no longer 

 exists. Under conditions to be created by works for the control of 

 floods the capacity of valley rivers for transportation of debris will be 

 increased, so that the mining might be partly resumed without preju- 



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