The construction, maintenance, or existence of unprotected or unbarricaded holes, pits, wells, building pads, or similar excavations which cause or are likely to cause a danger to life, health, and safety to the general public shall be prohibited. This section shall not, however, prevent any excavation which is required for the construction, remodeling, or expansion of structures or for industrial or farming operations, including the mining of sand and gravel, provided appropriate precautionary measures, such as the placement of warning signs, fences, etc., have been approved by the Zoning Administrator and placed on the premises. Nothing in this section shall apply to bodies of water, ditches, streams, or other major natural resources created or existing by the authority of the State of Michigan, Gratiot County, City of Ithaca, or other units of government. Excavation resulting from the extraction of sand, gravel, or other minerals for commercial purposes shall be required, upon termination of such activities and for a period of one year or more, to be refilled by the person, firm or corporation engaging in such excavation. The excavated site shall be graded and returned, as far as possible, to its natural state, including the planting of vegetation indigenous to the area.