California has its own exchange and has chosen a longer open enrollment period than the Federal administration. Covered CA (coveredca.com) is open for enrollment until January 31, 2018. However, if you want coverage beginning January 1, 2018, you must enroll by December 15, 2017.
Please note that if you are eligible for Medi-Cal, you can apply throughout the year.
There are many clinics and others who can assist you in applying for Medi-Cal, Covered California, or Healthy San Francisco. To find local help, enter your zipcode at https://apply.coveredca.com/hix/entity/locateassister/searchentities