they closed on the 15th last year (even though they re-opened the next weekend) because that's how the days set up in the middle of the month as they can't close on a weekday. So it wouldn't make much sense to close on the 13th (before the half mark of the month so it's too early) so the 20th only makes sense. Man, some of you are DUMB.
And yeah, they close on 420, big whoop? it's not as if that will really change anything on the mountain even if it is closing day.