Geologists--United States--20th Century, Geology--California--Nevada County, Geology--West (U.S.), Gold miners--United States--20th Century, Gold mines and mining--California, and Mining engineers--United States--20th Century
Geologists--United States--20th Century, Geology--California--Nevada County, Geology--West (U.S.), Gold miners--United States--20th Century, Gold mines and mining--California, and Mining engineers--United States--20th Century