Update: feedback from experts favors incesta, despite the very strong black bars at the base of each wing; a useful lesson...
This Libellula sp. was inside a small sunny patch inside the edge of woodland next to the San Jacinto River in easternmost Harris County; the fore-edge wing bars are dramatic; each wing has an obvious short black bar at the base (too strong for incesta?); the thoracic pattern seems wrong for vibrans; the face seems to be starting to darken slightly... could this be axilena?:
