Panoche Hills BLM: http://freecampsites.net/#!8690&query=sitedetails
It's too hot in the summer/this time of year, but winter/spring it's really beautiful, I was there last February to fabulous weather!
There is nothing around in any direction, anywhere, except I-5. So go prepared to boondock!
I spent a glorious 2 weeks there with Ferdy (my van, pictured above). My first night there, there was 2 other people, but the next day they all ran off, and I spent the next two weeks in solitude, with the occasional view of someone driving along a dirt road off in the distance.
With Love,
Tara