I just found out some marathon is taking place, and from their website:
"No cars, except local residents, will be allowed in the Cache La Poudre Canyon during the race."
The Colorado Marathon - Frequently Asked Questions
It says the race starts at 6:15am, and racers have 6 hours to complete it. That implies by 9:15am they should have cleared the first 15 miles of the canyon and they can open it back up yeah?
I sent an email to the race organizers, but I'm hoping someone here (maybe someone who lives in the canyon) will know what's up.