a steep-walled valley cut by a swift stream; deep, narrow ravine
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'gulch'prob. < dial., to swallow greedily < ME gulchen, of echoic orig.