Calaveras County, state and federal authorities are looking for ties between Monday night's pipe bombing in San Andreas and two similar incidents in other counties.

Since Monday morning, a pipe bomb was detonated in the Sacramento County city of Folsom in a garbage bin outside a shopping mall, and an explosive device was found and dismantled at the University of California Cooperative Extension in Woodland, in Yolo County.

Calaveras County Sheriff's Capt. Mike Walker said no links between the three incidents have been found but the probe continues.

"We are looking into that and any other type of bombings that have occurred," Walker said.

Meanwhile, about 35 Calaveras County Government Center employees returned to their offices this morning while the search for clues into who made and set off the bomb continued.

The pipe bomb exploded at 9:10 p.m. Monday behind the county Alcohol and Drug Abuse Program building. Investigators were on the scene from the time of the bombing until about 3 p.m. yesterday.

"It's been a long day," said Walker, who was at the scene from the time the bomb was reported until yesterday afternoon. He returned for morning briefings today.

Nobody has been named or taken into custody in connection with the bombing, which left a charred wall and some other structural damage but injured no one, Walker said.

Sheriff's officials are still looking for a white man, between 5-foot-6 and 5-foot-10, weighing 150-170 pounds. He had on a white T-shirt and dark pants and drove a newer, forest-green pickup.

The government center, at 891 Mountain Ranch Road in San Andreas, is the hub of Calaveras County's departments, programs and services.

The bomb blackened and stuck shrapnel into a wall and damaged an air conditioner and power box. The full extent of the damage won't be known until the siding, which needs replacement, is removed.