People shared photos and videos of the object on social media, wondering what it was and tagging NASA in their posts. They could not confirm if it was connected to the scrubbed rocket launch but said there is "no threat to the homeland".
"I was thinking it was a jet or something", Kira Bulger of Oakland told local CBS affiliate station KPIX 5. "Or aliens. One of the two".
There was speculation that the cloud-like formations seen Wednesday were also related to a rocket launch at Vandenberg.
The National Weather Service (NWS) suspects it might have been a meteor.
The Delta IV Rocket launch which was scrubbed was to be launched by United Launch Alliance (ULA) a joint-venture of Lockheed Martin and Boeing - they may attempt the launch again tomorrow evening.
We're just minutes away from the Delta IV heavy rocket launch that set to lift off at 5:49 p.m. from Vandenberg Air Force Base, according to the United Launch Alliance. The launch has been rescheduled for Thursday, the company reported.
"A bright meteor was visible in the skies over the Bay Area shortly after sunset", the organization wrote on Facebook. The society has already uploaded more than 40 images from people lucky enough to photograph the exciting event.
The American Meteor Society received more than 100 reports about the likely fireball event-dubbed 5618-2018-from sky watchers in Arizona, Oregon, Nevada and California.