SeaShells on beaches in San Diego?

I am going to San Diego sometime around next December or January. I was wondering this: what beaches are the best to collect neat seashells? At what time is it the best to find them? And..Is there anything other than clam shells? Considering I'm from SD (south dakota, not san diego!) I don't know anything really about tides and when they are so if that's a factor, when is low tide and when is high tide? Thank you for the help, this will make me finding beaches a lot easier!