First a little background. Medicare is the primary program for seniors and the disabled. It is paid for by taxes on employers and employees and administered by the federal government.
Medicaid is the primary program for the poor. It is paid for by the federal and state governments with taxes. Each state runs its own program and decides who and what to cover within federal floors and ceilings; 20 states (primarily in the South) have not yet expanded their Medicaid programs to cover all the poor with the funding available under the ACA.
About half of all Californians under 65 have employment-based coverage. The federal and state governments pay for about a third of the costs with a little understood mechanism known as pre-tax purchasing.
Individual coverage is partially paid for by the federal government with refundable tax credits and for the self employed with tax deductibility. The numbers of people with individual coverage have doubled due to the ACA.
The uninsured are people with none of the above coverage and no VA (Veterans Affairs) coverage. In California the numbers of uninsured have fallen very dramatically (more than half) due to the ACA. Undocumented Californians make up at least half of the remaining uninsured; they are not for the most part eligible for full scope Medicaid or for refundable tax credits.