The annual Hydrological Society meeting will be in Flagstaff on September 21 to 24. Also the AIPG (professional geologists) meeting is simultaneous. They have both workshops and some very interesting field trips.
I haven't checked out the pricing to see if it is possible to just go on a field trip or attend a lecture of interest without signing up for the whole conference. Included at the site is a "Phoenix to Flagstaff" geology road guide (pdf file) which is worth a look if you drive on I17.