This page from the March 29th 1990 edition of the Daily Gazette newspaper:
http://news.google.com/newspapers?n...3UhAAAAIBAJ&sjid=AokFAAAAIBAJ&pg=3000,6993579
says the timber trestle is 2460 feet long and was built in 1952.
Other research shows that the Benedict Bridge (Rt. 231) was definitely built in 1952. I wonder if that may have influenced the writer of the article who might possibly have mixed up the two bridges. I find it easier to believe that the Harper's Creek bridge would have been built when the base was built, in the later part of the 1940s.