The flash was seen in the clear Southern California sky about 8 p.m. Tuesday. It was visible more than 100 miles away, as far east as the Arizona line and as far south as the U.S.-Mexico border.
"From the description I got, it sounds like a very bright meteor or fireball as we call it," said Patrick So, an astronomer with the Griffith Park Observatory in the hills just north of downtown. He said it was mostly likely a fragment of an asteroid that broke up long ago.
Such objects give off a green glow as they burn up in the Earth's atmosphere, So said.
Trucker Tom Lawson was driving along Interstate 8 near Gila Bend, Arizona, when he says he saw "a green light with kind of an orange tail going from the southwest sky."
"It just kind of faded out as it got to the West Coast," he said.
Others said they witnessed the flash from San Diego and from Joshua Tree, in the Mojave Desert.