Officials noticed a crack forming in the 100 block of Woodridge Road about six feet from the northbound shoulder on Saturday afternoon, Hillsborough police Capt. Mark O'Connor said.
The crack widened as saturated ground beneath the northbound lane began to turn to mud and slip downhill, O'Connor said.
Slippage continued throughout the day Saturday until a 30-foot section of asphalt, mud and rock had fallen away from the road, exposing a 2-inch natural gas supply line and a 6-inch water line, O'Connor said.
As many as 22 public employees responded, O'Connor said, including an engineering team, police, water and sewer officials and Hillsborough Mayor Thomas Kasten.
Crews worked as weather permitted through Sunday, removing truckloads of debris and installing sheet pilings to stabilize the hillside.
Work will continue this week, O'Connor said. Woodridge Road will remain closed except to emergency vehicles until further notice.
O'Connor said the cost to reconstruct the road could go as high as $50,000 to $70,000.