Cal. Gov. Code § 32058

The board may require any pensioner retired for disability, under age 50, to undergo medical examination. The examination shall be made by a physician, appointed by the board, at the place of residence of the pensioner or other place mutually agreed upon. Upon the basis of the examination the board shall determine whether the pensioner is still physically or mentally incapacitated for service in the position held by him at the time of his retirement.