This photo was taken in August in Canon City, Colorado. The plant was growing in my dad's pasture near the head-gate, so that would be rich moist soil. The plant was over five foot tall.
Oenothera elata in Colorado
This is a detail of the flowers, seed pods, and leaves. It would have been showy if more of the flowers bloomed at once, but they slowly worked their way up the stock a few at a time.