Welcome to a great sport.
Most trapshooting veterans end up getting a 12 gauge over/under or single shotgun to use for trap. If you use a semi-auto, you’ll want to get a retention device to “grab” the ejected shells as it’s not polite to be hitting your neighbor with them. Also good for reloading, which will eventually reel you in as an adjunct to trap.
Check out the Browning lines (e.g. BT-99), Winchester 101’s, Remington, etc. You might want to get something used before you commit to a large purchase for something new. Go to www.gunbroker.com and you can find/buy something for transfer through your local FFL dealer. Getting a shotgun that’s sized properly for you is important; nominally, put the butt of the gun into your elbow (bent) and your fingers should be able to reach the trigger and grip.
I’m surprised that the State of California hasn’t banned lead for trap and skeet...yet. Good luck and welcome to a great sport.
(Former central coaster-Vandenberg AFB CA)