Some witnesses captured the event on video. The fireball has been described as a blue-green or yellow-orange light moving quickly across the sky at around 7:45 p.m. Wednesday.
NASA scientists say it was most likely a fireball - a fragment of an asteroid that entered Earth's atmosphere.
"Based on the reports we heard, a bright meteor was seen over much of the western, southwestern part of the country, California, maybe a little of Arizona and Nevada, maybe more," said Dr. Ed Krupp, director of Griffith Observatory.
"The description suggests that this was, in fact, a normal but bright meteor, the kind of thing that happens every now and then," Krupp said, adding that the Earth is hit with things from outer space often, mostly in uninhabited areas.
"For one of them to occur over an area like this and be this bright, you might see something like this once a year or maybe once every couple years," Krupp said.
Dr. Jenny Krestow, the lead astronomy professor of Glendale Community College, described the fireball as an "outer-space rock coming through the Earth's atmosphere."
"These things come in at tens of thousands of miles per hour. They come in so fast that they heated up a lot. They heated up so much that they started to glow. So what they saw was a glowing space rock," said Krestow.
Krestow said the object could have been the size of a fist or a human head but not much bigger.
Los Angeles City Councilman Tom LaBonge said he saw the bright light while on the road.
"I looked up, and I knew something was happening. I thought of Bill Haley. Bill Haley and the Comets," LaBonge said.
Scientists say these kinds of objects simply burn up in the atmosphere, posing no threat to us.