In what experts call "Flash Flood Alley," the terrain reacts quickly to rainfall steep slopes, rocky ground, and narrow riverbeds leave little time for warning.

With more than 170 still missing, communities must reconcile how to pick up the pieces around a waterway that remains both a wellspring and a looming menace.

Survivors have described the floods along the Guadalupe River as a “pitch black wall of death” and said they received no emergency warnings.