1925  Preparing the "spar-tree" for "high-lead," or "sky-line" rigging, is the most spectacular and thrilling performance in the logging industry.
1942  SKY LINE. In the case of a skidder, a heavy cable stretched from the spar tree out to a "back tree" at the far edge of the setting. A wheeled "bicycle" or carriage runs along this, bringing the logs from the woods when drawn by the skidding line, carrying the chokers back out to the waiting chokermen when drawn by the "receding line," which corresponds to the "haulback" of the yarder. In the case of a yarder the sky line is the same as the main-line, going from the spar tree through a block attached to a tree stump at the back of the setting, and is itself coupled directly to the haulback line.
1956  Matt [Hemmingsen] was also the man who rigged up the first skyline system ever used in the woods. This was in 1914 at Wardroper Bay on Cowichan Lake. . . .
1963  There's where the donkeys puff and strain As they pull the logs on the road And the skyline moans, as if in pain As it bears its heavy load.