T.s.tetrataenia´s should not be bred to any other specy nor subspecy!
Yes, some breeders tried that in Europe, forced by the fact, that ´tetrataenia was told to be the same as ´infernalis for a while some years ago. Because the limited number of avaliable California red sided breeders were inbred too the only success of this experiments were some lost branches at the pedigree ! No serious breeder like to cross in hybrids, and all breeders, who tried it or purchased some of the offspring were marked!
If San Francisco Garter Snakes are not grown and bred clean, they´ll lose any opportunity to refresh the natural populations later.

I´m sure T.s.tetrataenia will be extinct soon in all known habitats, if the government isn´t able to modify their enviromental policy!