If you mean in the ocean, no I don't believe that. I also live right on the coast in SoCal, and even here with the cliffs and secluded rocky coves, it would be very hard to hide a body. Waves action would likely move and expose a body.
Solana Beach? Even more unlikely I'd think to get her into the water, unless he had a boat and could go far out. Renting a boat would involve others.
I think Solana Beach was a diversion.
IMO, the dunes or somewhere inland is far more likely. There is a lot of undeveloped land.
Remember how long it took to find Amber Dubois? And she was only found a year later after her killer confessed and led LE to the site of her remains, somewhere inland north of Escondido. And, had her killer not killed another teen (Chelsea King), and was quickly apprehended, Amber may never have been found.