Brian,

Although I did not use Cutthroat Anglers, I did use information from the Keystone Chamber of Commerce for Nordic Ski instruction last winter. I was extremely satisfied, so I think the information they have about fly fishing would be just as helpful. Here is the link: http://keystone.snow.com/info/summer.other.flyfish.asp

This is a good resource for other things to do in Keystone.

Have fun!

Craig