After the fact, I found out that this was the "Running O' The Green" event. I was sitting in my living room when I saw the first half of this crowd passing by. There were actually twice as many runners as are seen in this video, but it took me awhile to get my camera working. I'm still trying to figure out where they all parked. There are only a dozen parking places at the trail head. It must have been a St. Patrick's Day miracle.