On 14 February 1975 the honorable William S. Spruill, Administrative Law Judge, approved the abandonment the Western Maryland Railway from Tonoloway, MD to Connellsville, PA. No appeals were filed and the decision went into effect on 11 April 1975.
I'm not sure this can be officially called the "Birthday" of the Great Allegheny Passage. Maybe it is more appropriately considered the conception.
It was indeed the day that the railroad officially closed, in the eyes of the Federal Government. However the rails were still in place and a few trains still plyed the route.
One notable train was the last passenger train from Connellsville to Hancock on 21 May 1975. That train introduced people to the idea of a long distance hiking/biking trail. It was a rail-to-trail project, well before the phrase "rails-to-trails" became popular.
Maybe the last train should be the "Birthday" of the Passage.
Actual trail wasn't built for for 11 years after the last train. In 1986 the Youghiogheny River Trail from Ramcat Hollow north to Ohiopyle opened. I don't have a date the trail opened since it was done quietly without a ribbon cutting or grand opening celebration. I guess Memorial Day of 1986 would do since that is traditionally a weekend that many people get out for a family ride.
Without a specific date, maybe we should just pick a good day in April or May and set that as the "Birthday", using 1986 the year. That would make the Passage 29 this year.
Maybe a Birthday or maybe just an interesting date, for now the 14th of February, along with being Valentines Day, is sill an important date in the history of the Great Allegheny Passage.