I am wondering under what circumstances can you step-up both halves of a spouse-inherited joint stock account?

I inherited stock from a joint tenancy stock account I opened with my husband in the late 1980s in the state of Oregon. We moved to California in 2002 and only reinvested dividends until his passing a few years ago. What tax basis do I use if I decide to sell the stock this year? Do I have to treat the original stock purchase and Oregon-based stock reinvestments as non-community-joint tenancy property and then treat the California reinvested stock purchases as community property? Or everything as quasi-community property? Lastly, and most importantly, am I allowed to step-up both halves or only his one-half to FMV on date-of-death?