Mohave County miner., 1916-11-11
.LINDGREN REPORTS
 ON SIERRA NEVADA
 AURIFEROUS GRAVELS

 has been mined from the tertiary i placer gravels of the Sierra Nevada of California is the subject of a report by Waldemar Lindgren, which has been published by the United States Geological Survey as professional paper 73.
 The Geological Surveys studies of the tertiary placer deposits of the California Sierra began in 1886 and were concluded about IS years later. During this period p quadrangular areas were Geographically mapped and IA of these were studied in geo. logic detail and the results published by the survey in geologic folios. Pro- fessional paper 73 includes the salient features of this earlier work, most of which was done by Mir. Lindgren him self. This report, thus comprehensive in geographic scope and minute in geologic detail, is believed to be the most complete and thorough descrip- tiOn of great placer gold province ever published.
 In the main the report is a detailed description of the entire area covered, including the gold placer gravels, but Mir. Lindgren's general account of the tremendous earth forces that built up the Sierra and of the processes that freed the gold from it's mother rock and brought about it's concentration in prehistoric river channels forms alto gether a most impressive description of continent building. Looking back ward through inconceivable vistas of time in which periods covering mil lions of years supplant the centuries by which we now now compute it's pas sage, the geologist pictures the up- lift of the newborn mountain range by upward-forced great bodies of molten granite. This uplift was ac- companied or closely followed by the formation of veins and seams of gold bearing quartz, and the resulting high land was then planed down by erosion caused by rainfall and the action of streams of water.
 Tracing the long course of this early history the geologist now finds that toward the end of what is known as tertiary time-a comparatively recent geologic period-volcanic forces that had long been quiescent vigorously re- asserted themselves. Flow of rhyolite, a volcanic rock, pouring from many craters, filled valleys that were GOV cred with gold-bearing gravel, deeply burying the gold and causing the for nation of new stream courses.
 The geologic events thus outlined long preceded the period of human history in which these metal deposits were mined. In 1S49 an army of gold seekers invaded the Sierra. They worked first along the present streams, but gradually the metal was traced to the old tertiary river beds on the summits of the ridges and to the quartz veins, the primary source of all the gold in the Sierra Nevada. Mil lions of dollars in gold were produced annually up to the '7Os of the last century, but the gold mining industry has slowly diminished, until now less than $1,0O0,OOO is produced annually, the decline being due to the prohibi- tion of hydraulic mining and the ex- haustion of the ric,,er channels suit able for drift mining.
 The total output of gold in Cali fornia is estimated at S1 200, 100000 to s1,500, 100000, about one-fifth of which has been derived from quartz veins, $3O0,0O0,000 from the tertiary gravels, and the remainder from the quater- nary deposits.
 A copy of professional paper 73 may be had free of charge upon application to the director, United States GeolnSi- cal Survey, Washington, D. c. The re- port is illustrated with photographs, diagrams and topographic and geo. logic maps.