Runner's Training Tips: training for a marathon altitude ?'s

Given the 5821' difference in elevation between Duluth and Durango (702' vs. 6523') I'd say you'll likely experience significant effects. Here's a link to some good information: http://www.personal.usyd.edu.au/~gerhard/pressure.html

Everyone is different in how they react to elevation change. As well, an indivdual may react differently each time he comes up to elevation. When I came up to Crestone for my Outward Bound course (from 500' ablove sea level) I was fairly fit (had been training for the course) and could barely run 2 miles, two days after arriving. You're probably in better shape than I was, but will still have some difficulty, I'd guess (Unless your one of the rare people who have no problem...). Fitness will help, often, but is no guarantee that you won't feel some effects. Keys to mitigating the effects of elevation change are to keep well hydrated, keep your eletrolytes up, and listen to your body. Ibuprofen helps as well. The first sign you're having problems with elevation change is typically a pretty good, generalized headache. Nausea and dizziness follow (often).

As for training, if your body will tolerate it I'd go ahead. It will feel hard (probably) but is one of those challenges runners tend to like ;). Bring water on your runs. I'd try trail runs that are easily reversible (not big loops). Durango is a great town, full of some terrrific opportunities for athletes.