crushed rock vs pit run

crushed rock and pit run both are nouns.

Word	Noun	Adjective	Verb	Adverb
crushed rock	Yes	No	No	No
pit run	Yes	No	No	No

As nouns, pit run is a hyponym of crushed rock; that is, pit run is a word with a more specific, narrower meaning than crushed rock:

Other hyponyms of crushed rock include ballast, bank gravel, pit-run gravel, shingle.

crushed rock (noun)	pit run (noun)
rock fragments and pebbles	gravel as found in natural deposits