I live in Santa Clarita and did a lot of my early training in Towsley Canyon. I did not know it at the time but the trail around Towsley is pretty good practice for Whitney type trails. Although Whitney is rockier.
Later I hiked Towsley through to Mentryville which is even more like Whitney terrain wise.
There are lots of hikes in the Hollywood Hills of course.
When you want to hike at altitute you're going to have to get in your car however. Mt. Pinos is good.
I also did a lot of stairs when training and more than anything on Whitney I was grateful for all the stairs I had climbed. Without the stair practice Whitney would have burned me out before the summit I think.
