On 14 June 2017, reports of an active shooter at Travis Air Force Base turned out to be a false alarm, a spokeswoman for the base told us.

The base, which is located in Fairfield, California, was placed on lockdown at about 3:20 P.M., after officials received a report of a shooter at the facility’s shopping center. CBS13 reporter Steve Large posted video in which the “real world” lock down was announced over the loudspeakers on the base:

At 5:17 P.M. local time, however, officials issued an all-clear, and no active shooter was found, according to Bobbie Textor, a base spokesperson: 

Officials responded to [the security incident] and it was determined to be a false alarm. Because of reports of potential gunshots outside base exchange, the base immediately responded to it.

The incident occurred as Travis Air Force Base was in the midst of doing exercises for just such a scenario, and also on the same day as two actual mass shootings in the United States.

Earlier in the day in Alexandria, Virginia, a gunman opened fire on Republican congressmen who were practicing for a charity baseball game at a park. Rep. Steve Scalise (R-Louisiana) was wounded along with three others, including a U.S. Capitol Police officer. Hours later, a gunman opened fire at a UPS warehouse in San Francisco. The shooter, who was wearing a UPS uniform, killed three people and wounded two before turning the gun on himself.

A third incident, which took place outside Barclays Center in New York City, stemmed from a dispute and ended with one man shot in the leg.

Sources:

KABC. “Travis Air Force Base in NorCal on Security Lockdown Due to Active Shooter Incident.”
  14 June 2017.

KOVR. “‘Active Shooter’ Reported at Travis Air Force Base.”
  14 June 2017.

Debolt, David. “Travis Air Force Base on Lockdown.”
  San Jose Mercury News. 14 June 2017.

Blankstein, Andrew, and Silva, Daniella. “San Francisco Shooting: Gunman Kills 3, Then Self at UPS Facility.”
  NBC News. 14 June 2017.