Green’s Dictionary of Slang

rocks and boulders n.

the shoulders.

1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.
1944		Maurer & Baker ‘“Aus.” Rhyming Argot’ in AS XIX:3.
1953		Berrey & Van den Bark Amer. Thes. Sl. (2nd edn).
1960		J. Franklyn Dict. Rhy. Sl.
1963		L.F. Freed Crime in S. Afr. 106: His ‘rocks and boulders’ [are] his shoulders.
1972		Dodson & Saczek Dict. of Cockney Rhy. Sl.