I have registered two different dirt bikes that had previously never been registered. It can be done, but it is a pain!
It would help if you have a bill of sale from the previous owner where the bill of sale indicates what state it came from and that that state does NOT register off road motorcycles. Make sure that is a true statement, however! It can get even more complicated if you say that the bike came from a state where it should have been registered as now the California DMV will want documents from the previous state.
If you get all the paperwork in order and have everything planned out ahead it will probably take two trips to the DMV (one with the bike) and one at the CHP (with the bike). I suspect that you could do it with one trip to DMV if you just went ahead did the CHP portion ahead of time instead of waiting for DMV to direct you there.
For the first trip to DMV you will need to make an appointment for a vehicle inspection. There are a few forms that you will want to download from the DMV website and fill out in advance:
Statement of fact #1: Basically saying that you are bringing this motorcycle into California and that it has never been registered anywhere before.
Statement of Fact #2: From the previous owner, saying that he owned the bike for such and such a period and it was located in x state and was never registered in that state.
Bill Of Sale: If you can, download the "Bill of Sale" form from the California DMV and have the seller fill that out.
"Application for Title or Registration": This is the main form and will need the approval of the DMV inspector, who will be looking at your bike.
Of course, the DMV inspector will look at your bike and record the VIN number and then ask a few stupid questions, such as "where is the smog label?" It really doesn't matter what answer you give him as it isn't going to fit in his procedure book and he/she will be new and thus has never done one of these before and after taking an hour to refer you to their supervisor they are going to direct you to the CHP so they can also look at the VIN number. The first time I did this I had the bike on a trailer and the inspector climbed up to inspect it. The second time they insisted that I unload the bike, so I had to go find a place to park where I could unload, push the bike 2 blocks back to DMV.
My experience is that the system the CHP has for making an appointment for having this inspection done is totally broken. You can call and they may tell you that no appointment is necessary, just come on in. When you get there they will tell you that the officer who does the inspections is only available on Wednesday mornings so you need to come back then. On Wednesday you arrive and they will tell you that you needed to have an appointment. The second time I did this I insisted on getting an appointment, then it worked smoothly. Unlike DMV, the CHP officer doing the inspection actually knows what he is doing and will probably have done a bunch of these before.
Once you have the form from CHP you will need to go back to DMV, but at least now you won't need to have the bike with you. If the pile of papers you are bringing in weighs at least one pound they will probably accept it and give you title to the bike. If you don't have enough forms and have jumped through enough hoops they will send you off to collect another worthless document, which they won't even bother looking at the next time you come back.
Personally, I have sworn to myself that I am never going to buy another bike that doesn't come with a clear title. Even an out of state title would be OK.
Rod