West Coast Wood Preserving

Found in California, Washington, Montana and in Milwaukee Road bridge timbers. These nails have a factory stamped WC followed by a hand stamped letter/date combination. According to "Date Nails Complete" by Glenn Wiswell and John Evans the P stands for "Pine" and the C stands for "Cedar".
WCWP ran two plants: one at Eagle Harbor, WA (built 1906, run by Pacific Creosoting Co., improved 1927), and one at Seattle, WA (built 1912, improved 1927) Quoted from Jeff Oaks "Date Nails and Railroad tie preservation" Volume III.