'Madge' really moved to San Francisco and became...
"Judy Barton" in Hitchcock's "Vertigo"!
"Judy" admits to having moved to SF from Salina, Kansas, three years prior.
"Picnic" was released in 1955, and "Vertigo" was released in 1958 - three years apart!
"Picnic" was partially filmed in Salina, Kansas.
In "Vertigo," we see what happens to the "Small-Town Beauty" when she moves to a much bigger pond: she ends up at the lower end of the food-chain.
She's lost much of her youthful appeal (even though she's still a stunner) - much in the same was as "Hal" ends up when he comes back to his own hometown.
"Don't call me 'honey', mac."
"Don't call me 'mac'... HONEY!"