J.C. O'BRIEN, 1952 ; MINES AND MINERAL RESOURCES OF DEL NORTE COUNTY; CALIF. JOUR. OF MINES AND GEOLOGY, VOL. 48, NO. 4 ; DIV. OF MINES, P. 295MAXSON, J.H., 1933 ; ECONOMIC GEOLOGY OF DEL NORTE AND SISIKIYOU COUNTIES: 29 TH REPT. STATE MIN.; CALIF. DIV. MINES, P. 147