The man arrived at his home in the 100 block of Marva Oaks Drive around 2 p.m. to find the front door kicked in, sheriff's Lt. Ray Lunny said.
The burglars, two men and a woman, were inside. They held the victim at gunpoint and restrained him, and tried unsuccessfully to open a safe, Lunny said.
The three eventually left, taking $350 from the victim, who was able to untie himself and call police.
Lunny said the suspects appeared to be familiar with the man's home because they knew where to find his safe.
Anyone who has information on the burglary is asked to call Sheriff's Detective Derron Sisneros at (650) 363-4055 or the Anonymous Tip Line at (800) 547-2700.