(Merged at this point into SH 55) When the U.S. Army built forts Clark (70 mi. SW) and McKavett (90 mi. NE) in 1852, this frontier trail connected the posts. After Fort Concho was established in 1867, the trail was extended farther north, to present San Angelo. It was later named for Col. Ranald S. Mackenzie, the 1873 commander of Fort Clark, who traveled it in his campaigns against hostile Indians. One of its landmarks was Mackenzie Lake (6.5 mi. N), which furnished water for the troops, for cattle drives up the trail, for settlers, and for Texas Rangers on frontier patrols. (1977)