30 years for the main lines but for the logging roads the geared engines were built for about a 10 year life. This was about the average life of most of the lumber companies, after 10 years all of the nearby trees were gone. The reason so many geared engines survived was due to the "baling wire artists" and blacksmiths who patched these rolling hardware nightmares back together after the woods crews destroyed them every season.
By the way, Roaring Camp's Heisler is only a month or two younger than the sad one still at Toulomne.