No weapons were found on Beaumont or in his car, but officials said they were concerned by statements he made, which they called "extremely unusual and alarming."
Police obtained a search warrant and found guns at Beaumont's home, including the AK-47 loaded with a 30-round magazine, an unloaded Uzi, two bolt-action rifles, three handguns and ammunition.
Beaumont's weapons were legally registered, police said, but the guns were taken by police as they investigate.
Tom Fleckenstein, deputy state's attorney for Anne Arundel County, said there was "no disqualifying prior that would prevent him from owning these firearms legally."
Beaumont was taken for an emergency mental health evaluation at Sheppard Pratt Health System, a psychiatric facility in Towson, Fleckenstein said. On Wednesday, a district judge revoked Beaumont's bond so he could be held for further mental health evaluation.
Fleckenstein said that "when he is done at the Sheppard Pratt," Beaumont will appear before a district judge.
The penalty for trespassing on posted property carries a 90-day maximum penalty, Fleckenstein said. Currently, he added, there are no additional charges against Beaumont.
Batten said Beaumont is being detained "on the mental health aspect that allows for law enforcement, who suspect that someone may be a danger to themselves or potentially to others, to hold them for safekeeping until such time that that person can be evaluated by medical professionals."