Band members tell ABC7 News' Luz Pena they saw the gunman coming near the food booths, in an area where hundreds of people were.
"It appeared he was shooting into the largest group of people he could find," said one band member.
The group says they hid under the stage after hearing "pop, pop, pop" and at least 20 shots.
They say, "You could smell the gunpowder, you could hear the screams."
A city official says three people died and 12 people were hurt during the shooting at the annual event.
The California food festival is a nationally known three-day event that attracts thousands of garlic lovers. Sunday was the final day.
Get the latest on the deadly Gilroy Garlic Festival shooting here.