California Code, Corporations Code - CORP § 5312

(a) Two or more persons may have an indivisible interest in a single membership when authorized by, and in such manner or under the circumstances prescribed by, the articles or bylaws subject to Section 5612; and

(b) If the articles or bylaws provide for classes of membership and if the articles or bylaws permit a person to be a member of more than one class, a person may hold a membership in one or more classes.