California's support centers are funded by the state bar through the Legal Services Trust Fund. The LSTF distributes Interest on Lawyer's Trust Accounts (IOLTA), Justice Gap, and Equal Access Funds.
From the California State Bar's FAQ page:
How is the IOLTA grant money distributed?
Answer: The law and State Bar rules and regulations set out specific guidelines for distribution of IOLTA. First, 85 percent of funds available for distribution is allocated to counties based upon their share of the state's more than six million indigent persons.
Within the counties, 10 percent of the money is reserved for projects that use pro bono attorneys (attorneys who volunteer their services without pay) as their principal means of delivering legal services.
Money not distributed to pro bono projects is divided among all other "qualified legal services projects" in that county, according to a statutory formula that is tied to each program's previous year expenditures. In order to be a "qualified legal services project," an organization applying for money must be a nonprofit corporation and must, as its primary purpose, provide civil legal services without charge to persons who are indigent.
Qualified legal services projects provide legal aid in a range of substantive areas: housing, healthcare, education, public benefits, consumer law, disability rights, and more.
The remaining 15 percent of available funds (the portion that is not divided among the counties) is distributed to "qualified support centers," meaning organizations that, without charge and as their primary purpose, provide training, technical and advocacy assistance on cases and other support to attorneys and paralegals employed by qualified legal services projects, as well as private attorneys who have accepted pro bono referrals from a legal services project.
These funds are distributed equally to eligible support centers that serve programs around the state. At present, 22 support centers share these funds.