CAL. PEN CODE § 519 : California Code - Section 519

Fear, such as will constitute extortion, may be induced by a threat, either:

1. To do an unlawful injury to the person or property of the individual threatened or of a third person; or,

2. To accuse the individual threatened, or any relative of his, or member of his family, of any crime; or,

3. To expose, or to impute to him or them any deformity, disgrace or crime; or,

4. To expose any secret affecting him or them.