The sinkhole was reported on Tassajara Road near the intersection with Silver Ranch Drive, according to Dublin spokeswoman Linda Maurer.
Tassajara Road is closed in both directions at the intersection, and crews are working to try to have the road reopened by later this evening after filling the hole with concrete, Maurer said.
She said authorities had originally hoped to have the road reopened in time for the commute tonight, but because of cold weather overnight, the curing process for the concrete is taking longer than expected.
The hole was apparently caused simply by wear on a road that was built a long time ago, according to Sue Stephenson, community affairs supervisor at the Dublin San Ramon Services District.
Investigators originally believed the hole, which was about 6 feet in diameter and at least 3 feet deep, had been caused by a broken water main, but that theory was discarded because of the lack of water in the hole, Stephenson said.
"It's an old creek that used to run through there, and it's an old county road," Stephenson said. "The way they made the road back then, things like this can happen when water seeps in from heavy rains and it comes apart."
Authorities have placed detour signs south of the sinkhole at the intersection of Tassajara Road and Gleason Drive notifying drivers of the closure, as well as north of the closure in unincorporated San Ramon, where Tassajara Road becomes Camino Tassajara, Maurer said.
Drivers are being detoured to Dougherty Road from Windemere Parkway in unincorporated San Ramon and Dublin Boulevard in Dublin.