Plague in CA is transmitted by biting insects which transmit the bacteria from rats. This is bubonic plague - not the highly contagious pneumonic form.
>Plague was first introduced into the United States in 1900. Between 1900 and 2012, 1006 confirmed or probable human plague cases occurred in the United States. Over 80% of United States plague cases have been the bubonic form. In recent decades, an average of 7 human plague cases are reported each year (range: 1-17 cases per year).
https://www.cdc.gov/plague/faq/index.html#
The three main antimicrobial agents recommended to treat plague are streptomycin, tetracycline, and chloramphenicol (1). Streptomycin remains the drug of choice, whereas chloramphenicol is most often restricted to the treatment of meningitis. However, due to the limited availability of streptomycin in some countries, gentamicin has been used as a substitute, and it was determined that gentamicin alone or in combination with a tetracycline could effectively treat human plague
https://aac.asm.org/content/50/10/3233#