Pecos River vs river

Pecos River and river both are nouns.

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

Pecos River (noun)	river (noun)
a tributary of the Rio Grande that flows southeastward from New Mexico through western Texas	a large natural stream of water (larger than a creek)