Cal. CIV § 3422

Except where otherwise provided by this Title, a final injunction may be granted to prevent the breach of an obligation existing in favor of the applicant: 1. Where pecuniary compensation would not afford adequate relief; 2. Where it would be extremely difficult to ascertain the amount of compensation which would afford adequate relief; 3. Where the restraint is necessary to prevent a multiplicity of judicial proceedings; or, 4. Where the obligation arises from a trust.