California income taxation.

State income taxation, generally, “piggy backs” on federal taxation.
The California Revenue and Taxation Code, for income taxes, makes copious references to the Internal Revenue Code (federal) and follows its content. Only when certain items differ from its taxation for state purposes, the California Revenue and Taxation Code will elaborate on such item. For example, when there is an entity that has income from sources out of California.

Indeed, the income tax returns for California ask for a copy of the federal tax return. The net income in that return is the starting point for filing the California return. Any differences are shown as adjustments to that net income. A large exception is the filing of personal tax returns for Domestic Partners. Domestic Partners may file a separate federal tax return as individuals, but they must file jointly for California.
NOTE:
Federal income taxes, employment taxes, excise taxes, and other taxes, are administered by the Internal Revenue Services. For the state of California, there are several separate agencies that administer taxation. depending on its type:

• Franchise Tax Board. For income taxes.  FTB.
• Employment Development Department. For employment taxes.  EDD.
• State Board of Equalization. For sales and business taxes.  BOE.
• County Assessor. For property taxes.
• Cities. For local business taxes.