It slammed into a vehicle and came very close to bystanders.
The balloon is part of a research project by professors and students at the University of California-Berkeley and several Taiwanese universities.
The project is to study gamma rays in space from 25 miles above the Earth.
The exact cause of the crash hasn't been determined, although wind gusts are suspected.
The team hopes to re-launch the balloon next month.
AP contributed to this report.