While on patrol in Bay Point Thursday night, some deputy sheriffs were stopped by a citizen reporting an assault with a deadly weapon, sheriff's office spokesman Jimmy Lee said.
The report led the sheriffs to a home in the 100 block of Bella Vista Avenue around 9:50 p.m.
During their investigation at the home, deputies found a loaded Uzi submachine gun on a bed, Lee said.
The discovery prompted deputies to call the Criminal Anti-Violence Support Effort team - a group of sheriff's deputies and California Department of Justice officers - to conduct a search of the home.
After obtaining a warrant, the team searched the residence and discovered 49 illegal shotguns, Uzis, rifles and handguns, Lee said.
The firearms were taken as evidence and deputies arrested a resident of the home, 50-year-old Mike Kestner, on suspicion of assault with a deadly weapon and for allegedly possessing the illegal weapons, according to the sheriff's office.
Kestner was taken to the Martinez Detention Facility where he is being held on $50,000 bail.