Best route from the Bay Area (CA) to Mammoth (CA)?

I think the Grapevine is 6% in places, and I have no issue with that. Highway 20 and Washington Rd. going in/out of the River Rest Resort are pretty steep too and I had no issues. That said, I just might go 80 because I don't want to get halfway into a trip and have to turn around. Plus, there are fun KOA/Casinos to stop at for a night around Boomtown/Reno. The only problem is that means 1 (or 2 if I stop on the way out too) extra nights that aren't in Mammoth.

-TJ