Did you examine the seedheads? It's hard to tell from the photo. They could be in Lamiaceae and have small seeds, but it looks like there are remnants of ray petals, so a close up of a seedhead showing the seeds would help. Perhaps some coneflower Ratibida, or Gaillardia? Asteraceae.

Or perhaps a Rudbeckia?

Rudbeckia was implied under coneflowers. The most common in the Dallas area are R. hirta, R. fulgida, R. amplexicaulis and R. maxima. The height rules out maxima, too many ray petals for amplexicaulis, that leaves hirta and fulgida. Sure resembles Rudbeckia hirta.