There is hereby granted to the Montana Power Company, a corporation, its successors and assigns (hereinafter called the "grantee"), the right, privilege and franchise for the full period of fifty (50) years from and after September 21, 1980 and thereafter until and unless otherwise provided by ordinance to construct, equip, lay, maintain and operate in, under, upon, over and across the streets, avenues, alleys, highways, bridges, easements and other public places in the city, as now or hereafter constituted, mains, pipes, conduits, manholes, reducing and regulating stations and all other appurtenances and accessories for the purpose of transporting, conveying, distributing, supplying and selling natural gas or artificial gas, or a mixture of natural and artificial gas for light, heat, power and other purposes, at rates fixed and allowed by the public service commission of Montana, and grantee agrees to file with the city clerk, the schedule of rates thus fixed and allowed. (1983 Code § 13.02.010)