The Collaborative International Dictionary of English v.0.48:

Coulee \Cou`lee"\ (k??`l?"), n. [F. coul['e]e, fr. couler to run
   or flow.]
   A stream; (Geol.) a stream of lava. Also, in the Western
   United States, the bed of a stream, even if dry, when deep
   and having inclined sides; distinguished from a ca[~n]on,
   which has precipitous sides.
   [1913 Webster]