Re: Maximum grade for NG RR lines?

Loggers may not have had engineering degrees but they were ingenious on their own and sometimes had engineering companies lay out the logging railroad system. In the Pacific Northwest one such engineering company that specialized in working with the logging companies to design efficient logging rr systems was a company called Thomas and Meservey. Sometimes maps are still extant that were made by companies such as this showing the layout proposed. Carrying this a step further regarding steep grades, I know of one engineered logging system in which a mainline system was built along a ridge line with grades suitable for a rod engine. Another mainline was built across meadow land at the bottom of the multiple small canyons radiating down from the ridge line. It appears to me that they likely took the empties off the ridge mainline down spurs built in the canyons which were very steep. The loads would always being going down grade and not even empties had to be pulled up the steep canyon bottoms. This allowed the spurs to be at the extreme of gradient short of a tram line or rack railroad.