This cache is a younger brother to 'An Anagram of ROCK' by 2 Leg Drive. That cache, now sadly archived, was disguised as a cork in a cork forest so, guess what, this is disguised as a rock in a quarry.
Be careful - cliffs in the vicinity! In fact, if you are on a cliff you are in the wrong place.
Thanks to JayOmegaTor for some historical information from the National Archives https://mildenhall.moadoph.gov.au/photo/4186 Great research.