70  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  FART   T. 
CONCLUSIONS   REGARDING   COLUMBIA   RIVER   GOLD. 
Nearly  all  the  sands  in  the  bed  of  Columbia  River  and  on  the  adjoin- 
ing terraces  and  benches  throughout  the  region  covered  by  this  exami- 
nation carry  some  fine  gold.  The  relative  amounts  have  not  been 
accurately  determined,  though  the  statements  of  miners  and  pros- 
pectors indicate  that  the  low  bars  in  the  river  bed  contain  more  gold 
than  the  deposits  on  the  benches. 
The  average  width  of  the  river  is  about  1,500  feet,  and  it  is  probable 
that  a  considerable  part  of  its  bed  from  one  side  to  the  other  is  covered  • 
by  sands  and  gravels  containing  some  gold.  The  gold-bearing  ter- 
races are  not  continuous  on  either  side,  being  absent  for  long  stretches, 
nnd  it  may  be  safely  estimated  that  if  distributed  so  as  to  be  con- 
tinuous they  would  make  a  strip  of  land  not  exceeding  300  feet  on* 
each  side  of  the  river. 
Many  of  t lie  richer  spots  were  discovered  and  worked  out  by  Chi- 
nese, and  there  is  no  record  of  the  a  mount  of  gold  they  obtained. 
Moreover,  the  observations  described  in  this  report  were  not  sufficient 
to  justify  a  close  estimate  of  the  amount  of  gold  remaining.  It  would 
seem  a  liberal  estimate,  however,  to  put  the  average  width  of  the 
gold-bearing  areas,  including  the  river  bed  and  benches,  at  2,400  feet, 
the  thickness  of  the  gold-bearing  deposit  at  6  feet,  and  the  amount  of 
placer  gold  originally  contained  within  such  limits  at  1  cent  per  cubic 
yard.  On  these  terms  the  total  amount  of  gold  contained  in  the  river 
bed  and  adjacent  benches  did  not  exceed  $28,000  per  linear  mile,  and 
the  total  amount  in  the  90  miles  between  Kettle  Falls  and  Nespelem 
did  not  exceed  $2,500,000. 
This  gold  is  not  uniformly  distributed,  but  in  very  small  areas  is 
concentrated  enough  to  justify  mining,  especially  where  rich  deposits 
occur  in  the  bed  of  the  Columbia,  since  the  comparatively  cheap 
process  of  dredging  is  here  available.  The  bench  lands,  however,  are 
not  adapted  to  any  relatively  inexpensive  process  of  mining.  Hydrau- 
licking  on  a  large  scale  is  ruled  out  by  the  absence  of  bed  rock  and 
the  scarcity  of  water  at  sufficient  elevation;  dredging,  by  the  height 
of  these  deposits  above  the  river  and  the  impossibility  of  floating  the 
machinery  over  them.  Moreover,  the  possible  profits  from  mining 
the  bench  lands  would  undoubtedly  be  less  than  the  value  of  these 
lands  for  agricultural  purposes. 
