Rod -
To risk the obvious - why don't you just go hiking? as opposed to doing stadium stairs? The desert ranges - Inyos, Panamints, Cosos, etc are great places for winter hiking. Some of the best hiking in SoCal is in DV, and it's just cooling down enough now to make it sane. And there's lots of peaks and hills within an hour of Santa Clarita.
And Bee - you asked for suggestions - I don't know where in Northern CA you live, but if you want to get in shape for hiking - why don't you just hike? So-called "core work" is fine, I suppose, but don't over-analyze this - nothing puts you in shape for hiking but hiking. If you want to be in good shape for Whitney, then do 2-3,000' of elevation gain/loss on the weekends between now and you'll have few problems making the summit or any other 14'er.
