river vs Pecos River

river and Pecos River both are nouns.

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

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