172  OOMRtBtfTtOKS    TO   ECONOMIC    GEOLOGY,  1903.  [bwa.226. 
main  vein  strikes  about  N.  70°  W.,  and  dips  53°  NE.  Years  ago, 
when  the  stamp  mill  and  the  chlorination  plant  were  running,  the  ore 
was  removed  through  a  1,200-foot  tunnel,  from  which  drifts  extended 
on  the  vein  for  1,500  feet  at  a  level  of  500  feet  below  the  croppings. 
From  the  tunnel  level  an  incline  was  sunk  on  the  vein  to  a  depth  of 
1,050  feet  below  the  outcrop.  The  greater  values  were  found  toward 
the  eastern  end  of  the  mine  near  the  surface,  in  the  neighborhood  of 
a  dike  of  andesite-porphyry,  which  cuts  the  siliceous  rocks  of  the 
region  and  is  intersected  by  the  vein.  The  Riley-Bliss,  Clipper,  Beien, 
and  other  quartz  prospects  in  the  vicinity  of  Uncle  Sam,  are  doing  little 
now,  the  greater  activity  being  confined  to  the  adjacent  deposits  of 
copper  ore.  On  Dog  Creek,  however,  -1  miles  west  of  Delta,  just 
beyond  the  western  border  of  the  quadrangle,  the  Inca  mine  is  ship- 
ping assorted  ore  in  bags. 
GOLD  AND   SILVER  OF  COPPER  MINES. 
By  far  the  greater  part  of  the  gold,  and  particularly  all  of  the  silver 
of  the  Redding  quadrangle,  as  shown  in  the  table,  comes  from  the  cop- 
per mines.  The  oxidation  of  the  pyritiferous  copper  ores  near  the 
surface  formed  the  gossan  which  characterizes  such  bodies.  Leaching 
removed  the  copper  but  left  most  of  the  iron  in  the  form  of  limonite 
and  with  it  the  bulk  of  the  gold  and  silver,  so  that  in  the  early  days 
the  mines  were  opened  and  worked  for  gold  and  silver  before  the 
copper  values  at  greater  depths  were  discovered. 
COPPER. 
The  brief  account  of  the  copper  deposits  of  the  Redding  region  pub- 
lished in  United  States  Geological  Survey  Bulletin  No.  213,  pages  123- 
132,  will  here  be  supplemented  by  additional  general  observations  on 
some  of  the  lodes  and  prospects  and  the  progress  in  mining  during 
the  year.  The  term  lode  is  used  to  include  all  the  ore  bodies  in 
essentially  the  same  shear  zone.  In  the  copper  region  they  are  rarely 
as  much  as  100  feet  in  width  and  a  mile  in  length,  and  several  may 
occur  in  each  ore-bearing  tract  within  a  district. 
Within  a  decade  California  has  come  into  prominence  as  a  copper 
producer,  and  is  now  the  fourth  in  the  rank  of  States.  The  greater 
part  of  this  mineral  wealth  comes  from  the  Redding  quadrangle  or 
close  to  its  borders.  During  1903  the  mines  and  man}^  prospects  in 
all  districts  of  the  copper  region  have  been  active,  and  the  time  is 
approaching  when  the  output  will  be  greatly  increased. 
IRON   MOUNTAIN    DISTRICT. 
The  largest  and  most  active  district  of  the  copper  region  is  that  of 
Iron  Mountain.     As   yet   the   only  producing   part   of   this  district 
