Cal. Health & Safety Code § 103480

If the time and place of birth are not known, the court shall receive and consider evidence and testimony as may be available and from the facts adduced may, by order, fix the time and place that the court finds to be a probable time and place of birth of the person in relation to whom the petition has been filed, as the time and place of birth. The time and place so fixed shall thereafter for all purposes be the time and place of birth of the person.