The Beach Girls and the Monster (1965) opens with The Watusi Dancing Girls from the famed Whisky a Go Go dancing on a Santa Monica beach. This exemplar of psychotronic filmmaking weighs in at just one hour and six minutes but manages to pack in plenty of monster action, surfing, stilted dialog, and "no fewer than 13 different sections of full-bore, deep-reverb tank surf instrumentals" according to the book Pop Surf Culture.
Watch it for free on the Internet Archive!