Police deputies were called around 4 p.m. to reports of an armed robbery at the recycling center behind the store on West Napa Street, the sheriff's department reported.
The victims reported that a white male and a Hispanic male with handguns demanded money and mentioned that they had a machine gun, the sheriff's department reported.
The suspects took the victims' money and fled north on Fifth Street West in a black sports car with the rear license plate concealed.
Sheriff's department deputies and a helicopter joined police to search for the suspects, who were spotted about a half hour later in the Agua Caliente area of the county.
A deputy then located the black Mitsubishi Eclipse around 4:35 p.m. in the area of state Highway 12 and Arnold Drive and began a pursuit driving west on the highway.
Deputies witnessed a handgun being thrown from the vehicle near Nuns Canyon Road, the sheriff's department reported.
The suspects, identified as Napa resident Ramon Llamas, 19, and a 16-year old Napa boy, then came to a stop near Dunbar Road and were arrested.
Investigators allegedly recovered the pistol thrown from the vehicle in the area of Nuns Canyon Road, the sheriff's department reported.