Update, 1:40 a.m.: San Dimas Sheriff's officials identified two men arrested in the May 2 warrant service in the 1100 block of East Gladstone Street.
Arrested were father Richard Elmo Pack, 62, and son Richard Reese Pack, 31. Both men were arrested on suspicion of possessing illegal weapons. The son was additionally charged with possessing a controlled substance for sale.
The father and son are being held in lieu of $20,000 bail.
"In total they found two pistols and three assault rifles and the drugs," said Lieutenant Andy Berg. The quantity of the drugs allegedly seized was not known, but there reportedly was enough for authorities to believe there was intent to sell.
The warrant served at the location was part of a specific investigation of both the father and son and was not part of a Countywide probation operation as first believed, Berg said.
The Los Angeles County Sheriff's Special Enforcement Detail was on scene specifically to deal with the possibility of assault weapons being at the location, authorities said. Authorities had a big presence Wednesday, blocking off a large swatch of Gladstone while the SED served the warrant and arrested the two men.
Both men are expected to be arraigned at West Covina Superior Court the morning of May 4.
Previously: Members of the Los Angeles County Sheriff's Department served a search warrant today on a house near the corner of Gladstone Street and Willow Avenue.
Not very many details are known at this time. The activity was possibly part of a countywide probation compliance enforcement operation, according to officials at the San Dimas Sherrif's Station. However, no one from the San Dimas Station was involved in the operation, according to Lieutenant Andy Berg.
Officials at the scene would not reveal the nature of the warrant being served, or who was arrested during the operation, but at least one man was seen detained by authorities.
It appeared members of the County Sheriff's Special Enforcement Detail were on scene during the operation.
Glendora Police were summoned to help block off traffic to the area around 7:40 p.m.. Traffic along Gladstone Street from Sunflower to Willow Street was closed, including traffic along Willow Street.
Authorities may have been in the area prepping for the arrest most of the day. A resident reportedly observed Sheriff's patrol cars driving around the neighborhood since the morning hours.
"They said 'something's going to be going down … but it's not in your area, so don't worry about it.' The first one I seen go through here was at 8:30 this morning. They had everybody, they had a SWAT Team," the resident said.
This story will be updated as information becomes available.