river vs Cimarron River

river and Cimarron River both are nouns.

Word	Noun	Adjective	Verb	Adverb
river	Yes	No	No	No
Cimarron River	Yes	No	No	No

river (noun)	Cimarron River (noun)
a large natural stream of water (larger than a creek)	a river that rises in northeastern New Mexico and flows eastward into Oklahoma where it becomes a tributary of the Arkansas River