@adamengst I learned of the following Black Diamond Trail closure today, copied from https://ithacatrails.org/trail/black-diamond-trail/
NYS Parks will be working on the section of the Black Diamond Trail between Perry City Rd. and Garrett Rd. from Monday, September 21st, through Friday, October 2nd. During this time, this section of the trail will be closed to all patrons Monday through Friday, with NO ACCESS. The trail will reopen for normal use on the weekend between these dates (September 26-27th).
Unfortunately the Black Diamond Trail Challenge course’s turnaround is right in the middle of this trail section, meaning we will be unable to run it from either end during the closure dates. Note that the closure does not affect the Run Rabbit Run route, which only uses the BDT north of the closure.