Timber trestles were one of the few railroad bridge forms that did not develop in Europe. The reason was that in the United States and Canada cheap lumber was widespread and readily available in nearby forests. The Pacific Northwest of the U.S. and the province of British Columbia, Canada became the central region for hundreds of logging railroads whose bridges were almost all made of timber Howe trusses and trestles.
Timber trestles generally come in two forms. The first and most common is the pile trestle which consists of bents spaced 12 to 16 feet apart. Each bent consists of 3 to 5 round timber poles that are pounded straight into the ground by a pile driver. The centre post is upright, the two inner posts are angles at about 5 degrees and the outside posts are usually battered, angling outward for stability at about ten degrees. During construction, the top of the uneven posts are cut to the proper level for a cap which in turn supports the stringers and planks that hold the rail. Taller pile trestles contain diagonal "X" bracing across one or both sides of the bent and also between bents.
For higher timber trestles, the framed bent is used. Unlike pile bents, frame bents usually use square timbers and rest on mud sills or sub sills that act as a foundation. Frame bents are built in a series of "stories" that are usually between 10 and 50 feet high. For extremely high trestles, each section of the bent is built flat on the ground as a single or double story and then lifted and placed onto the ever lengthening trestle.
None of the dozen or so highest timber bridges of all time exist anymore. Nearly half of these 200 foot high monsters were built for logging railroads in the U.S. state of Washington and on Vancouver Island in British Columbia, Canada. For the lumber industry, rail lines were usually little more than a web of dead end tracks blanketed across the contour lines of a forested mountainside. Once the terrain was logged out, the tracks were abandoned. Since lumber was easy to find and abundant, it could quickly be cut on-site into tall piles or bents. With nothing built to last, construction standards were often low. Expensive bridges, especially those made of steel, were avoided by the loggers.
Early timber bridges had their drawbacks. Untreated lumber only lasted about 20 years and locomotives could easily cause the wood to catch fire. Collapses - rare today - were a regular occurrence on logging railroads and there are numerous accounts of train crews that regularly hopped off their slow moving locomotive as it approached a high, untrustworthy trestle, allowing it to cross before they would then run across the bridge and jump back on. On main lines that carried passengers and freight, tall timber bridges reduced efficiency as trains had to cross them at slower speeds. Initially they were a quick way to get the route open but once established, the owners usually had them replaced with steel bridges or filled.
Without trestles to bridge the "gaps" the logging companies would have had a hard time. Trestles, in more ways than one carried the logging industry. Look at the pictures (left and right) of these two incredible trestles.
Club member Mike Tadlock's profession is a forester. Club members were fortunate enough to be taken into the Ten Mile Basin to see the remains of a trestle that was built over 100 years ago. As the pictures in the gallery left attest, the redwood pilings are still in excellent condition.
Club member, Mike Aplet, recently sent me pictures (click thumbnail right to of other small trestles belonging to Caspar Lumber Company's operations. In his e-mail accompanying the pictures Mike indicated how he came by them:
"We did a hike with a group of Willits High School kids last memorial day weekend. Our group hiked the Old Trestle Trail which is on the South Fork of the Noyo in the Camp 1 area…… This section followed the creek all of the way up the canyon nearly to the ridge. ……. As you can see, Mother Nature is slowly taking back what is hers."
After I expressed my thanks for the pics Mike sent me another picture taken near Three Chop Ridge.
Mike explained in his e-mail, "Another relatively easy hike in Jackson State Forest is the hike down Three Chop Ridge in the Indian Springs area. It is marked as Road 330 on the JSDF maps (Click here to see map). There are remnants of many trestles all along the ridge line. This was one of the ridge top rail spurs that were only connected to the main line by incline. Walking along this ridge it is easy to see that most trestles were not the grandiose 50- 75-100 foot structures but rather ones that usually were no taller than about 6 ft. tall. Where ever there was a dip in the natural grade, it was easier for the early railroaders/loggers to simply build a trestle to bring their tracks to constant grade rather than trying to move a lot of earth."