Michael wrote saying
"The brown would turn blue in a few hours.
Based on the pattern
and what I can make out of the terminal appendages,
my best guess is Enallagma civile (Familiar Bluet),
but it could also be Enallagma ebrium (Marsh Bluet)
or Enallagma hageni (Hagen's Bluet).
The mid-September date is also good for E. civile."