Any cemetery authority not exempt under chapter 68.40 RCW shall establish, maintain, and operate an inviolable endowment care fund. Endowment care, special care, and other cemetery authorities' endowment care funds may be commingled for investment and the income therefrom shall be divided between the funds in the proportion that each contributed to the sum invested. The funds shall be held in the name of the trustees appointed by the cemetery authority with the words "endowment care fund" being a part of the name.