I have a fair amount of desert hiking experience -- Utah, Arizona, California, Texas, and the more arid sections of Washington state. (Yes, Washington does have desert areas, though we often associate Washington with rain) However, I have never undertaken such a long hike in such conditions. I have never had to to carry so much water. I have never been more nervous about a hike.
The Southern California region winds through a fair amount of diverse terrain. The elevation varies between 1200 and 9000 feet, through dry hills, mountains, forests, dusty desert-land, and the San Andreas fault zone. The trail climbs into and traverses the San Jacinto mountains, San Bernardino and San Gabriel ranges, and finally into the Tehachapi Mountains.
I'll keep you all informed as to how it is!