I am a former california resident who hasn’t lived there since the legalization. From talking to friends of mine who use it for Ulcerative colitis, my understanding of the process is this:

I believe that either, you can have the prescription written by your normal M.D. (in this case your rheumatologist), or, you can have a letter written by that M.D. documenting your condition to the M.D. at the marijuana dispensery. At the dispensery they have a physician who will write you the prescription. I do not think you need to bring a copy of your chart. The letter will at least suffice for the first few prescription/doses. They will discuss with you for further doses/prescriptions if you need to make it more official.

A letter on letterhead stating “I have seen (name) for # years for treatment of chronic lupus and rheumatoid arthritis. I am a board certified rheumatologist, yada yada yada.
Dr. X” was all that my friend required.

I personally would get the letter, and then let the physician at the dispensery make the prescription for the marijuana so that if you decide to get your chart forwarded to another physician in another state, etc. or you switch insurance companies and get employed in another state, the prescription is not in there. That way, also, you don’t have to be in the uncomfortable situation of having to ask your dr. to write you that scrip (if you think it is uncomfortable.)

Good luck