This request isn't all that easy to grant. Skiing in Southern California is not all that bad, but it's not like CO, UT or even Tahoe. However, the beaches are great. Look into Orange County for that desire. Tahoe is pretty far from the beach and the beaches in Nothern California are much rockier and the water demands a wet suit (or even a dry suit) due to colder temps. If you live in Orange County and want to travel to Mammoth you are looking at about a 5-6 hour drive to get there.
If you really want to ski big mountains and surf in the same day you will have to move to New Zealand, or Monaco (apparently).
I can only speak for so cal because that's where I am from but...
What he's saying is pretty spot on. I gerew up in north orange county, but I skied the most when I was in college going to Cal Poly Pomona. Our ski/snowboard club would several times a year do the "perfect day" thing and ride in the morning and go to the beach in the afternoon. Pomona was 40 mins from Baldy, about and Hour from Mtn. High and 1:45 from Bear and about an hour from Newport so I would say it is one of the more centrally located places in So. Cal to riding and surfing. To be honest though going and doing both activities in one day is tiring and unless you go to mtn. high you have to deal with some degree of mountain driving (and if it snows at all plan on at least doubling you drive time).
My last year in college I did weekend trips to mammoth nearly every weekend from october until august. If you don't mind driving, the drive isn't bad at all, I would average about 5:15 to 5:30 from my house in Pomona to Mammoth. To me Tahoe was just a little too far for just a weekend trip (don't get me wrong I love skiing there, but I only go about 3 times a year), not to mention driving around the lake can be slow at times. The only thing is that doing that can be ratehr costly unless you have a place to stay and a very economical car.
Northern and central california (except the coasts) would probably be much more affordable than so cal, but I feel if you really want to ride and get the beach atmosphere that you seem to be looking for so cal might be the answer.