river vs Platte River

river and Platte River both are nouns.

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

river (noun)	Platte River (noun)
a large natural stream of water (larger than a creek)	a river in Nebraska that flows eastward to become a tributary of the Missouri River