A  GOAL  PROSPECT  ON  WILLOW  CREEK,  MORROW 
COUNTY,  OREGON. 
By  W.  C.  Mendenhael 
The  coal  prospect  here  described  is  on  Willow  Creek,  about  22  miles 
above  Heppner,  the  county  seat  of  Morrow  County,  Oreg.,  in  a  rather 
mountainous  region  just  west  of  the  divide  between  the  Willow  Creek 
and  the  John  Day  River  drainage.  The  coal  property  is  in  sees.  33, 
34,  35,  and  36,  T.  4  S.,  R.  28  E.  Willow  Creek,  a  tributary  of  Colum- 
bia River,  flows  through  a  canyon  from  its  source  to  its  mouth,  but 
this  canyon  deepens  toward  the  head  of  the  stream  because  the  gen- 
eral level  of  the  surrounding  country  is  higher  in  this  direction.  The 
elevation  of  the  bed  of  the  creek  in  the  vicinity  of  the  coal  prospect  is 
about  4,400  or  4,500  feet  above  sea  level.  That  of  the  highest  sum- 
mits near  by  is  perhaps  7,000  feet. 
The  walls  of  the  lower  portion  of  Willow  Creek  canyon  reveal  sec- 
tions of  basalts  exclusively.  These  rocks  underlie  the  central  por- 
tion of  the  Columbia  River  valley,  and  are  probably  to  be  correlated 
with  the  Yakima  basalt  of  central  Washington.  Eighteen  or  20  miles 
above  Heppner  the  geology  changes  abruptly  and  older,  altered  rocks, 
including  basic  plutonics  and  granitic  and  diabasic  intrusives,  appear 
in  the  canyon  walls.  These  rocks  clearly  represent  a  part  of  the  base- 
ment upon  which  the  lavas  were  poured  out  and  their  abrupt  appear- 
ance is  probably  to  be  explained  by  the  presence  of  a  sharp  fault  of 
perhaps  a  few  thousand  feet  throw,  with  the  uplift  on  the  eastern  side 
of  the  fracture.  Just  below  the  coal  mines  coarse  feldspathic  sand- 
stone outcrops,  overhang  the  older  basement  rocks  and  dipping  in 
general  20°  or  25°  SE.,  the  strike  of  the  sedimentary  beds  being  north- 
east and  southwest  with  local  variations  in  attitude.  This  belt  of 
sediments  is  reported  to  have  been  explored  for  15  or  20  miles  along 
the  strike  and  to  extend,  therefore,  to  the  southwest  across  the  divide 
into  the  John  Day  drainage  basin.  Overlying  the  sedimentary  beds 
the  basalts  appear  again,  capping  the  neighboring  ridges.  The  total 
thickness  of  the  sedimentary  section  here  was  not  measured,  but  by 
combining  the  apparent  exposed  section  above  the  creek  bed  with  the 
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