The hole, in the median of the highway, was spotted about midnight Thursday by a construction worker involved in a repaving project, officials said. One lane in each direction was shut down, although the highway remained open, The Sacramento Bee reported.
Rochelle Jenkins, a spokeswoman for the California Department of Transportation, said the westbound lane opened in mid-morning and the eastbound one in mid-afternoon. The hole was filled with concrete.
Jenkins told the Reno (Nev.) Gazette-Journal the department had been unable to measure the depth of the sinkhole. She said it was almost certainly caused by water, possibly from cracks in a culvert in the area or from groundwater not gathered up in the culvert.
"It has been developing for a while, not something that developed over the week," she said.
Sinkholes most commonly develop in limestone, which can dissolve leaving underground hollows, like the one that swallowed a lake near Ocala, Fla., this week. They can also be the result of human activity.
A large sinkhole that opened this week in southern Louisiana was believed to be a collapsed salt dome cavern.