If the district is authorized to acquire, develop, operate, and maintain inland parks and recreation areas, at least 75 percent of its annual expenditures shall be devoted to that purpose until such time as the total expenditure of district and county funds for land, structures, and improvements which is used for inland park and recreation purposes shall have equaled the total expenditure of district and county funds for land, structures, and improvements which is used for beach and harbor purposes. Thereafter, the district shall devote at least 50 percent of its annual expenditures averaged over each five-year period for inland park and recreation purposes.