Avoid Santa Monica at all costs. The freeway going from the valley (which is on the way from SFMM) to Los Angeles will be completely closed off that weekend, so access to L.A. will be extremely limited and tedious. You'd be better off going to Ventura and going to the beach there. I'm not certain which freeways you'd need to take, but I know that it's possible, not ridiculously far away, and will save you time since you wont have to deal with the major freeway closure.