Legal Question in Criminal Law in California

If by 'scare off' you mean you got caught and cited by F&G for 'hunting' turkeys on public land with a high power hunting slingshot, then yes, it could be 'illegal', as evidenced by the court citation.

If you are asking if you can spook them of your property by throwing rocks, of shooting small pebbles with a kids toy slingshot, that would not likely be 'hunting' or 'illegal'.