This page, entitled "Bridge Inspection - Timber Trestles", lists a number of steps involved in inspecting timber trestles using humourous cartoons and text. ca. 1940s.
Yukon Archives. James Y.C. Quong fonds, 2005/31, Box 3, 3/8/7. Bridge Dept. Northwest Highway Maintenance Establishment. Bridge Maintenance Data. Courtesy of the Estate of J.Y.C. Quong/ Printed with Permission