Is dinosaur national monument a proper pronoun?

No, Dinosaur National Monument is a noun, a proper noun, the name of a specific place on the Colorado Utah border. A proper noun is always capitalized.

A pronoun is a Word that takes the place of a noun in a sentence. The pronoun that takes the place of the noun Dinosaur National Monument is 'it'.

Example: We visited the Dinosaur National Monument on our trip. It contains many dinosaur fossils.