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.

The Guadalupe River has a history of deadly flooding. Here is a look over the decades. (AP video Marshall Ritzel/Albee Zhang)

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.

As the Guadalupe River swelled from a wall of water heading downstream, sirens blared over the tiny river community of Comfort — a last-ditch warning to get out for those who had missed cellphone alerts and firefighters going street-to-street telling people to get out.