Civil Code § 1198

1198.

The execution of an instrument may be established by proof of the handwriting of the party and of a subscribing witness, if there is one, in the following cases:

1.When the parties and all the subscribing witnesses are dead; or,

2.When the parties and all the subscribing witnesses are non-residents of the State; or,

3.When the place of their residence is unknown to the party desiring the proof, and cannot be ascertained by the exercise of due diligence; or,

4.When the subscribing witness conceals himself, or cannot be found by the officer by the exercise of due diligence in attempting to serve the subpoena or attachment; or,

5.In case of the continued failure or refusal of the witness to testify, for the space of one hour, after his appearance.