For Men:
Suits and slacks. Tuxedos optional.
Groomsmen in tuxedos.
For Women:
From full-length gowns to cocktail attire.
Bridesmaids in full-length gowns.
Denver International Airport (DIA) is about 90 minutes from the wedding venue by car.
Lyons is a very small town about 20 minutes North from Boulder/Longmont.
Various accommodations are listed here.