Man-made fibres are to be distinguished from natural fibres such as silk, cotton, and wool. Natural fibres also consist of polymers (in this case, biologically produced compounds such as cellulose and protein), but they emerge from the textile manufacturing process in a relatively unaltered state. Some man-made fibres, too, are derived from naturally occurring polymers.
Mount Si is located in North Bend, Washington (USA). The climb is 4,167 feet (1,270 meters) and 4 miles from the parking lot to the summit plateau. Vertical elevation change is about 3700 feet and starts at about 700 feet. The route meanders through several different ecosystems as temperatures and average rainfall vary with elevation.
The V-shaped gap serves as a gateway to the west. The base of the gap is about 300 feet (91 m) above the valley floor below even though the north side of the pass was lowered 20 feet (6.1 m) during the construction of Old U.S. Route 25E.