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.

Ten teenagers were killed after being swept away by rising floodwaters from the Guadalupe River while evacuating their summer camp in July 1987, according to the National Weather Service. (Credit: NWS

PolitiFact | Cloud seeding could not have caused the disaster because the process increases precipitation only by a small amount, experts said.

More than 100 deaths have been reported statewide, with most near the Guadalupe River. Several girls from the Dallas area are among the deaths confirmed from Camp Mystic.