Thanks for your report, Adrian!
I checked eBird records for that coppery, pugnacious "dyno-mite," and "the book" is almost correct.
There are a few records in June from Mancos and the Durango area, and a few for early July, plus
many records for mid and late July, of course.
The book is absolutely correct if you consider that for Rufous Hummingbirds, migration south
can begin in June and early July. So I suppose the book refers to the hummers' southward migration season,
not the usual autumn months many birders think of when you mention "fall migration."
Your report is valuable! Do you have specific dates in June when it visited at your feeder? If so, please
submit your observations to eBird. Birders near you can coach you if you are not yet "an eBirder."
Joe Roller, Denver