Where in California do you live?
If you live in a desert town, such as Barstow, California City, Etc. then I could see a dual sport bike.
If what you are really interested in is MX and expect to go to the track and start hitting the jump, a dual sport bike just isn't going to cut it.
First off, to be legal on the street you need to have D.O.T. approved tires, which will just suck off road and you absolutely will NOT survive a MX track with them. If you try to ride your off road knobbies on the asphalt you will be buring through $80 tires every week.
To be legal on the road you will also need mirrors and turn signals. These will also not survive the spills you are 99.99% likely to have riding off road.
If you are just interested in riding some trails and not get too wild you can get by with the D.O.T. tires and a nice dual sport bike. Definately buy one already plated as it can be a very difficult process to deal with the DMV.
Like others have said, fill out the "sticky" found at the top of the "which bike do I get?" forum and we can help steer you towards the right bike.
Rod
Rod