Cal. Prob. Code § 811

(a) A determination that a person is of unsound mind or lacks the capacity to make a decision or do a certain act, including, but not limited to, the incapacity to contract, to make a conveyance, to marry, to make medical decisions, to execute wills, or to execute trusts, shall be supported by evidence of a deficit in at least one of the following mental functions, subject to subdivision (b), and evidence of a correlation between the deficit or deficits and the decision or acts in question:
1. (1) Alertness and attention, including, but not limited to, the following:
  1. (A) Level of arousal or consciousness.
  2. (B) Orientation to time, place, person, and situation.
  3. (C) Ability to attend and concentrate.
2. (2) Information processing, including, but not limited to, the following:
  1. (A) Short- and long-term memory, including immediate recall.
  2. (B) Ability to understand or communicate with others, either verbally or otherwise.
  3. (C) Recognition of familiar objects and familiar persons.
  4. (D) Ability to understand and appreciate quantities.
  5. (E) Ability to reason using abstract concepts.
  6. (F) Ability to plan, organize, and carry out actions in one’s own rational self-interest.
  7. (G) Ability to reason logically.
3. (3) Thought processes. Deficits in these functions may be demonstrated by the presence of the following:
  1. (A) Severely disorganized thinking.
  2. (B) Hallucinations.
  3. (C) Delusions.
  4. (D) Uncontrollable, repetitive, or intrusive thoughts.
4. (4) Ability to modulate mood and affect. Deficits in this ability may be demonstrated by the presence of a pervasive and persistent or recurrent state of euphoria, anger, anxiety, fear, panic, depression, hopelessness or despair, helplessness, apathy or indifference, that is inappropriate in degree to the individual’s circumstances.
(b) A deficit in the mental functions listed above may be considered only if the deficit, by itself or in combination with one or more other mental function deficits, significantly impairs the person’s ability to understand and appreciate the consequences of his or her actions with regard to the type of act or decision in question.
(c) In determining whether a person suffers from a deficit in mental function so substantial that the person lacks the capacity to do a certain act, the court may take into consideration the frequency, severity, and duration of periods of impairment.
(d) The mere diagnosis of a mental or physical disorder shall not be sufficient in and of itself to support a determination that a person is of unsound mind or lacks the capacity to do a certain act.
(e) This part applies only to the evidence that is presented to, and the findings that are made by, a court determining the capacity of a person to do a certain act or make a decision, including, but not limited to, making medical decisions. Nothing in this part shall affect the decisionmaking process set forth in Section 1418.8 of the Health and Safety Code, nor increase or decrease the burdens of documentation on, or potential liability of, health care providers who, outside the judicial context, determine the capacity of patients to make a medical decision.