IDAHO.  131 
RELIEF  AND  DRAINAGE. 
The  relief  and  general  topographic  features  are  similar  to  those  of  the  Coeur  d'Alene  min- 
ing district.  The  elevations  range  from  about  7,000  feet  at  Wards  Peak  to  about  2,100 
feet  at  the  lowest  point  within  the  district,  on  St.  Joe  River.  Seen  from  the  mountain  tops 
the  region  has  the  aspect  of  a  rolling  plateau  dissected  by  canyons  to  a  depth  of  1,000  to 
3,000  feet.  This  plateau  is  regarded  as  a  peneplain  produced  by  the  erosive  action  of  streams 
and  rivers  when  the  land  surface  stood  at  a  lower  elevation.  At  that  time  the  principle 
drainage  channel  was  in  a  broad  valley  having  about  the  same  general  position  as  St.  Joe 
River.  After  the  formation  of  this  old  surface  the  whole  region  for  many  miles  both  north 
and  south  of  this  district  was  elevated  as  a  great  block,  from  which  the  Coeur  d'Alene  Moun- 
tains have  been  carved. 
The  floor  of  the  old  valley,  which  in  places  was  deeply  gravel  covered,  has  been  elevated 
to  an  average  height  of  1,000  feet  above  the  present  river  bed  and  dissected  with  the  remain- 
der of  the  plateau,  leaving  a  series  of  gravel-capped  hills.  All  the  rivers  and  creeks  lie  in 
narrow  canyons.  They  are  characterized  by  steep  gradients  and  comparatively  large  vol- 
umes of  water.  St.  Joe  River,  the  large  trunk  stream  of  the  district,  has  a  broad  bowlder- 
strewn  bed  through  most  of  its  length,  with  occasional  narrow  flood  plains  and  gravel 
benches.  At  two  points  the  walls  of  the  valley  contract,  forming  what  arc  locally  called 
"box"  canyons.  The  upper  of  these  canyons,  which  lies  just  west  of  the  crossing  of  the 
De  Borgia  trail,  contains  several  waterfalls  and  marks  the  head  of  canoe  navigation.  Many 
of  the  tributary  streams  head  in  small  glacial  lakes  on  the  flanks  of  the  higher  mountains 
at  elevations  above  5,000  feet.  Their  canyons  contain  few  deposits  of  gravel  or  sand  and 
in  them  the  bed  rocks  are  usually  exposed.  Owing  to  their  high  gradients  and  volumes 
many  of  the  streams  could  be  used  for  water  power,  and  a  few  water-right  locations  have 
been  made,  though  in  no  case  has  a  power  plant  been  installed. 
GEOLOGY. 
The  prevailing  rocks  of  this  district  comprise  a  series  of  arenaceous  and  argillaceous 
sediments,  which  as  a  whole  show  little  contrast.  Nearly  all  the  beds  are  characterized  by 
shallow-water  features.  The  rocks  are  identical  with  those  making  up  the  series  exposed 
in  the  Cceur  d'Alene  district,  which  have  been  examined  with  great  care  by  Ransome  and 
Calkins.a  They  are  of  Algonkian  age  and,  as  exposed  in  the  area  of  the  Coeur  d'Alene 
special  map,  have  a  thickness  of  about  15,000  feet.  The  series  comprises  six  formations, 
differing  slightly  from  each  other,  which,  arranged  in  order  from  the  top  of  the  series  down, 
are  called  the  Striped  Peak,  Wallace,  and  St.  Regis  formations,  Revett  quartzite,  Burke 
formation,  and  Prichard  slate.  Although  in  the  St.  Joe  region  the  rocks  have  been  exam- 
ined only  in  hasty  reconnaissances,  it  seems  probable  from  the  observations  made  that  all 
the  formations  distinguished  by  Ransome  and  Calkins  in  the  Coeur  d'Alene  district  are  rep- 
resented. The  structures  also  are  nearly  if  not  fully  as  complex.  The  rocks  are  intensely 
folded,  the  dips  varying  from  nothing  to  90°  and  the  prevailing  strikes  being  about  west- 
northwest.  Overturned  folds  have  been  noted  in  a  few  instances  and  faulting  is  a  common 
feature.  Most  of  the  faults  strike  approximately  west-northwest  and  east-southeast,  par- 
allel with  the  prevailing  strikes  of  the  bed  rock,  though  some  having  an  approximate  north- 
south  direction  have  also  been  recognized,  and  in  a  number  of  instances  a  well-developed 
joint  system  also  striking  northwest  and  southeast  was  observed.  In  the  northern  part  of 
the  district  the  rocks  are  unaltered,  and  only  the  softer  beds  are  affected  by  slaty  cleavage. 
In  the  southern  part,  however,  from  St.  Joe  River  to  the  southern  limit  of  the  region  exam- 
ined, the  rocks  become  progressively  more  schistose,  the  softer  beds  especially  being  altered 
to  mica-schists,  often  studded  with  garnet  and  staurolite.  All  gradations  between  the 
unaltered  sediments  of  the  northern  part  of  the  district  and  these  schists  can  be  observed. 
o  Ransome,  F.  L.,  Ore  deposits  of  the  Coeur  d'Alene  district,  Idaho:  Bull.  U.  S.  Geol.  Survey  No.  260, 
1905,  pp.  277-285. 
