Only capitalise it as part of a proper noun, such as naming a specific national park, not when writing about national parks in general. We decided to visit some national parks on our holiday.
Capitalize specific names of geographic locations (cities, streets, states, countries, etc): Huck Finn fished in the Mississippi River. no caps – He fished in the river. Capitalize names of specific places and institutions (businesses, schools, buildings, parks, etc.)
Note: plateau, when used alone, is lowercase. Use “the Grand Canyon” on first reference and “the canyon” on subsequent mentions. Note: canyon, when used alone to refer to the Grand Canyon, is lowercase. Use “the Colorado River” on first reference and “the river” on subsequent mentions.
“National” should only be capitalised when used as or part of a proper noun, or at the beginning of a sentence. You are using it as an adjective.
In general, you should capitalize the first word, all nouns, all verbs (even short ones, like is), all adjectives, and all proper nouns. That means you should lowercase articles, conjunctions, and prepositions—however, some style guides say to capitalize conjunctions and prepositions that are longer than five letters.
A proper noun is the specific name of a person, place, organization, or thing. All proper nouns (as well as adjectives derived from them) should be capitalized.
When “California State Parks” (or just “State Parks”) refers to a branch of government (the Department of Parks & Recreation), it should be capitalized and used as a singular proper noun.
Likewise, ordinary job titles in isolation are never capitalized. For example, the job title in “The park ranger asked for our permit” is a mere description, and needs no emphasis. Job titles are at times absurdly attenuated, and placing them before a person’s name can wear readers out.
Ocean gets capitalized because it is part of that puddle’s proper name. It’s not an Atlantic ocean, it’s the Atlantic Ocean.
Few things scream bureaucrat like capitalizing the word city at every opportunity. City is not a proper noun, and should not be capitalized like one. New York City is a place name and a proper noun that includes the word city.
Lowercase the general term national anthem, which can refer to any country’s patriotic song. Capitalize “The Star-Spangled Banner,” the U.S. national anthem written by Francis Scott Key.