One of the best places in the U.S for this exact combination is Boulder, Colorado. Multiple outfits with fantastic trekking in the foothills of the Rocky Mountains. Amazing flying with at least 5 very good schools renting the latest and greatest. You could get a mountain checkout and experience hot and high performance stuff. Fly to the highest airport in the U.S (Leadville, KLXV) which is a short flight from Boulder. Field elevation just shy of 10,000ft.
Direct flights from LHR to Denver on BA. Boulder is just a 30 minute drive from Denver Airport.
If you need any advice or contacts let me know as I live part of the year here and part in Ireland.
All the best.