Can I be fired without a reason in California?

Usually yes. Labor Code section 2922 presumes California employment is at will, so an employer may terminate without cause or notice. Termination is still unlawful when motivated by a protected characteristic under Government Code section 12940, by retaliation for protected activity such as whistleblowing under Labor Code section 1102.5, or in violation of public policy.

Usually yes, but never for an illegal reason. Labor Code section 2922 presumes California employment is "at will," so an employer may terminate without cause or notice, and an employee may quit the same way. The presumption has hard limits. Termination is unlawful when the motive is a protected characteristic (race, sex, age over 40, disability, religion, sexual orientation, and others under Government Code section 12940), or retaliation for protected activity: reporting suspected legal violations (Labor Code section 1102.5), complaining about wages or harassment, taking family or medical leave, or filing a workers' compensation claim (Labor Code section 132a). Courts also recognize termination in violation of public policy, firing someone for refusing to break the law or for serving on a jury. Contracts and union agreements can replace at-will status with "good cause" protection. The label "at will" therefore begins the analysis; the employer's real motive ends it.

Authority: Cal. Lab. Code § 2922