   the grand canyon of the yellowstone is the first large canyon on the yellowstone river downstream from yellowstone falls in yellowstone national park. the canyon is approximately  long, between  deep and from  wide.nps:grand canyon of the yellowstone ==history== although trappers and prospectors who visited the yellowstone region had knowledge of the canyon, the first significant descriptions were publicized after the cookâfolsomâpeterson expedition of 1869 and the washburn-langford-doane expedition of 1870. when charles w. cook first viewed the canyon after traveling west from the lamar valley on september 20, 1869 he subsequently wrote these words in his journal: i was riding ahead, the two pack animals following, and then mr. folsom and mr. peterson on their saddle horses. i remembered seeing what appeared to be an opening in the forest ahead, which i presumed to be a park, or open country. while my 
Canyons_and_gorges_of_Wyoming Hot_springs_of_Wyoming Landforms_of_Park_County,_Wyoming Landforms_of_Yellowstone_National_Park Visitor_attractions_in_Park_County,_Wyoming