About 1923, a log cupola cabin became the first structure on Middle Sister. A 35' wooden tower with L-4 cab replaced it in 1951, but was accidentally burned in 1953. The present 30' treated timber tower with L-4 cab, built in 1954, is staffed most summers. It is listed on the National Historic Lookout Register. There was also a patrol lookout tower 1 1/2 miles northwest atop West Sister until 1954.