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.

Also: San Antonio mourned the victims in a Travis Park vigil; UTSA said one of its teachers died in the Guadalupe River flood; Kerrville officials said a privately owned drone collided with a helicopter conducting search and rescue operations.

The region of Texas where flash flooding killed more than 90 people -- including dozens of campers -- is known for its tendency to experience flood emergencies.

Flash flooding is common enough around the crescent-shaped region from Dallas through the Hill Country, the area earned the nickname "Flash Flood Alley."

Plans to develop a flood monitoring system in the Texas county hit hardest by deadly floods were scheduled to begin only a few weeks later.

At least 120 people have been found dead since heavy rainfall overwhelmed the river and flowed through homes and youth camps in the early morning hours of July 4. Ninety-six of those killed were in the hardest-hit county in central Texas, Kerr County, where the toll includes at least 36 children.

Over just two hours, the Guadalupe River at Comfort, Texas, rose from hip-height to three stories tall, sending water weighing as much as the Empire State building downstream roughly every minute it remained at its crest. The force of floodwater is often more powerful and surprising than people imagine.