These lights originally appeared as 1st Range through 5th Range in the List of Lights, but they were later given the following official names: Poste-Saint-Martin, Rivière Valin, Rivière du Caribou, Savard Range (replaced by Simard Range in 1912), and Rivière-du-Moulin.
After being improved in 1875, the front range tower stood twenty-six feet tall and exhibited its light at a focal plane of twenty-six feet, while the rear tower stood forty-three feet tall and exhibited its light at a focal plane of forty feet. The two fixed white catoptric lights were separated by 910 feet.
In 1907, the early range lights were replaced by a new pair of towers. The following description of these towers appeared in the Annual Report of the Department of Marine:
Poste St. Martin range lighthouses Saguenay river, were replaced by new towers and the old towers torn down. The front tower now stands 650 feet back in the line of range from the site of the old front tower, and about 100 feet back from high water mark. It is a wooden building, square in plan, with sloping sides surmounted by a square wooden lantern, the whole painted white. The height of the tower from its base to the top of the ventilator on the lantern is 47 feet. The light is a fixed white light, elevated 47 feet above high water mark, and visible 7 miles in the line of range. The illuminating apparatus is catoptric.
The back tower stands 2,060 feet from the front tower. It consists of a skeleton steel frame, square in plan, with sloping sides, painted brown, surmounted by an inclosed wooden watchroom and a square wooden lantern. The watchroom and the lantern are painted white. The height of the tower from its base to the top of the, ventilator on the lantern is 82 feet. The light is a fixed white catoptric light elevated 81 feet above high water mark and visible 7 miles in the line of range.
The front wooden tower was erected by contract by Mr. G. Bergeron, of Poste St. Martin, for $597, and the back steel tower was purchased from Messrs. Goold, Shapley & Muir, of Brantford, Ont., for $668.50. The erection of the steel tower was performed by day’s labour, under the supervision of the Quebec agency, and cost $1,367.22.
Sometime before 1995, a pair of skeletal towers that display an orange trapezoidal daymark with a black vertical stripe were erected for Poste-Saint-Martin Range. Instead of being separated by 2,060 feet, the new range lights are located 10,900 feet or over two miles from each other. The front light remains in its historic location on the south shore of the Saguenay River at Poste St. Martin, while the rear tower now stands atop a bluff on the north side of the river.