You were loaded open carrying on unincorporated land and they stopped you?
I'd call the CalGuns Foundation since you were subject to a 12031(e) check where 12031 did not apply, and thus you were unlawfully seized and searched without any reason. http://www.calgunsfoundation.org/cgf-hotline.html
You were right about the unlawful detainment and you were right about the sidesaddle being loaded. The cop was misinformed or being willfully ignorant.