The victim was identified Tuesday as Nancy Rogers, 61, of Fremont.
Rogers was reported missing Monday morning just before 5 a.m., from her workplace at the post office on Santa Clara St. in Hayward, Hayward police lieutenant Chris Orrey said.
Investigators discovered a trash bin at the post office had recently been dumped. Police contacted Waste Management of Alameda County and discovered that a trash collector had picked up the bin some time before the employee was reported missing, according to Orrey.
They went to the landfill and searched the piles of trash, where they discovered the worker's body, police said.
Police and investigators are looking at surveillance video in the search for clues to the woman's death. Waste Management, U.S. Post office staff and the U.S. Postal Inspectors are helping Hayward police with the investigation.
Bay City News contributed to this report.