It's not the miles its the kind of miles.
No matter what you do in SoCal you will not replicate the MMWT, especially the elevation and trail above Mirror Lake. The best you can do is get close to the mileage and gain in SoCal. The Mt. Baldy and San Gorgonio areas are best. You can get 6,000' gains and 22-mile trips at both with a little imagination.
However, you should plan on a trip to White Mountain in June. This will give an idea on what it like to hike over 11,500' and what it takes to get 14,000'. White Mountain is an easy 14er...so they say.
