California Code, Water Code - WAT § 2551

(a) During the investigation of the stream system, the representatives of the board shall investigate in detail the use of water by each person who has given notice of intent to file a proof of claim, and shall determine the acreage under irrigation or otherwise define the place of use and purpose of use, determine the location and capacity of the 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.

(b) In conducting investigations under this article, the board shall consider all pertinent information, including, but not limited to, information provided under Sections 1840 and 1841.

(c) Representatives of the board may conduct a field investigation of a person's water use after giving 30 days' notice in writing to the person subject to the investigation, or at the request of that person as part of the investigation of the stream system.  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.