I believe it closed the weekend after the hike in Jason's report. I can't remember the reason exactly, but something to do with critter mating. We passed a sign about halfway to three quarters up the grade stating this. Below that point is open year around. The trail system information page has no mention of closures and talks about cross country skiing. This would lead me to believe that only the upper portion near Perins Peak and the mine is closed off during winter.
I seem to recall that it opens sometime around late spring or early summer.
-Jon