Those little lines were popular for large construction projects in the era before heavy trucks became reliable and usable on unpaved roads. Common for hauling aggregate for big dams in the late 1800s-1920s or so, from a quarry or pit often located in the area where the lake would eventually be. Occasionally all the equipment would be left there to be flooded and discovered decades later when a drought drained the lake - not worth dragging back out. The track and equipment was small and light enough to be dragged to the site with mule or horse teams, perhaps in pieces for assembly there.

Similar stuff was used in the salt ponds in San Francisco Bay until relatively recently, because the track was easy to pick up and move around. Lots of youtube movies - especially in Europe where they were sometimes used both in industrial plants (even relatively small ones) and institutions like old folks homes. Gauges were typically around 2' or metric equivalent. Think, also, lines in mines and between the mine mouth and a mill. By the 1930s trucks could handle that kind of work and use of the temporary lines mostly ended.