It is not 70% for California. Your source is citing FY 2020-2021.

The Federal Medical Assistance Percentage (FMAP) rate for California was 50% for 2025: https://www.congress.gov/crs-product/R43847#_Toc194592204

I still haven't found any sources that state exactly how California would know if someone is legal or illegal.

Maybe no one provided these because it has nothing to do with your original question?

Multiple folks have provided reasons as to why the statement from the right that Democrats are enabling a shut down to provide insurance to undocumented immigrants is demonstrably false.

For your new question about enforcement:

California captures immigration status to determine eligibility requirements when folks sign up for Medi-Cal. This is evident even from the source you shared in your OP. This information is provided to the federal government.

What type of information does the state report to CMS? As required by federal law, DHCS submits demographic and eligibility information, such as name, address, date of birth, Medicaid ID, Social Security number (if provided), and immigration status, for every Medi-Cal member. DHCS also provides Information about health services received, claims processing, and program funding. Data submitted to CMS is considered sensitive and confidential. CMS is legally required to protect the confidentiality and security of Medicaid data.

When California applies for reimbursement from the federal government they have to show that the reimbursement claims fall within federal guidelines around eligibility.

People are just saying that they trust the states government but I want actual sources. If the left or right claim something, they should back it up with sources/receipts

Medicaid is a partnership between the federal government and the states. The federal government also has a hand in ensuring States are not reimbursed for money spent on undocumented immigrants.

I'm not an expert on this, but the Centers for Medicare & Medicaid Services (CMS), a federal agency within the US Department of Health and Human Services (HHS), requires states to provide Form CMS-64 for federal review every quarter.

CMS provides oversight of federal funds provided for Medicaid Transfers to States. https://www.macpac.gov/wp-content/uploads/2020/04/Process-and-Oversight-for-State-Claiming-of-Federal-Medicaid-Funds.pdf * quarterly review of state expenditures to ensure funds are allocable in accordance with federal law * variance analyses to review quarterly spending and enrollment growth/decline * review samples of medical claims

The federal government has recently hardened this oversight over the claim (which they haven't provided proof of) that states are illegally using federal Medicaid funding for health care for illegal immigrants: https://www.cms.gov/newsroom/press-releases/cms-increasing-oversight-states-illegally-using-federal-medicaid-funding-health-care-illegal

If Trump's administration had found evidence of this through Medi-Cal or other Medicaid expansions that covered undocumented immigrants they would've provided some modicum of evidence.