Article X, § 4

All taxable property except as hereinafter in this section provided, shall be assessed in the county, city, township, village or district in which it is situated, in the manner prescribed by law. The property, including franchises of all railroads operated in this state, and of all express companies, freight line companies, dining car companies, sleeping car companies, car equipment companies, or private car line companies, telegraph or telephone companies, the property of any person, firm or corporation used for the purpose of furnishing electric light, heat or power, or in distributing the same for public use, and the property of any other corporation, firm or individual now or hereafter operating in this state, and used directly or indirectly in the carrying of persons, property or messages, shall be assessed by the state board of equalization in a manner prescribed by such state board or commission as may be provided by law. But should any railroad allow any portion of its railway to be used for any purpose other than the operation of a railroad thereon, such portion of its railway, while so used shall be assessed in a manner provided for the assessment of other real property.