WordNet records no synonym and no antonym for colorado plateau. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a large plateau to the south and west of the Rocky Mountains; abuts mountains on the north and east and ends in an escarpment overlooking lowlands to the south and west; the Grand Canyon is carved out of the southwestern corner
Synonyms, antonyms and the broader and narrower relations for colorado plateau come from Princeton University’s WordNet. Full sources and licences.