The National Weather Service began sending flash flood warnings that should have triggered cellphone alerts a little after 1 a.m., while local officials began posting on Facebook about four hours later.

Rescuers searched the Guadalupe River for survivors of the Texas floods that killed more than 100 people over the July Fourth holiday weekend, with an unknown number of people still missing. The basin area was crowded with families and campers preparing to enjoy the holiday when pounding rain brought about catastrophic flash floods just before dawn Friday.