The location of the rock art along the St. Louis River trail is reported in distance from specified bollards. What are bollards? Bollards are vertical posts used to control vehicle traffic. On the St. Louis River trail, the bollards are steel pipes setÂ into the middle of the trail, near roads, parking lots, etc. The bollards are about 4 feet high and about 3.5 inches in diameter. They are yellow with three red and silver stripes near the top. The bollards were selected as reference points because they are not likely to move and they will be easy to see, even if there is groundcover, such as leaves or snow.