Such a great area. Living in CO, I still have not backpacked there though it's high on my to-do list. It's FAR from Denver (6+ hrs) so we've been there as car tourists only.
Couple things:
- The Chicago Basin area is the classic backpacking place. Info:
https://sjma.org/area-info/chicago-basin-trip-planning-guide/trip-planning-for-backpackers/
- There are many other hiking and backpacking opportunities.
- Late Sept, be prepared for snow. Labor Day, be prepared for hordes. In between can be paradise.
- If the monsoon lasts longer than typical, it may be wet. But would not let that dissuade you.
- Biggest thing is the incredible drought in that area this year. The San Juans got 20% of their typical snowfall last year, leading to extreme fire risk, forest closures (like you can't go in to the National Forest right now!) and a big fire called the 416 fire which basically now occupies half of the west side of US 550 between Durango and Silverton. The train is not running right now. The fire is mostly under control but has had devastating consequences this summer for the tourist season.
- The monsoon which is starting this week (really in the past 3-4 days) may change much of this, with typical good rains for the next 4-6 weeks.
- So don't change any plans yet, but stay tuned, especially regarding forest closures and camping restrictions.
Enjoy!