Cal. Wat. Code § 2551
During the investigation the representatives of the board shall, after 30 days' notice in writing to each person who has given notice of intent to file proof of claim, conduct a detailed field investigation of such person's use of water, and shall determine the acreage under irrigation or otherwise define the place of use and purpose of use, determine the location and capacity of such person's diversion works and conduits conveying water from the stream system, and the amount of water diverted and reasonably required to satisfy the uses being made. It shall be the duty of each claimant to be present at some time during the detailed field investigation either in person or by an agent who is authorized to sign the proof of claim.
Ca. Water Code § 2551