Bridges... the fastest way to make them used to be just dropping a log across a cleft. This is the only untrussed log bridge I've ever seen with a train on it, made of just two logs.

the Minnetonka was the Northern Pacific Railroad's Locomotive No. 1.

 Built in 1870, it was first used in northern Minnesota, then brought to the the Olympic peninsula for use in logging.

Photo taken in the mid 1880's

The bridge is just two long logs spanning the river with sufficient structural strength to support the track, locomotive and railcars full of big logs.

http://www.blackdiamondnow.net/black-diamond-now/2016/10/the-minnetonka-circa-1885.html