An officer was responding to an unrelated call in the 700 block of Rockwell Place at about 8 p.m. when he turned a corner and encountered two men in an unlit area of open space.
One of the men was holding an illegal shotgun partially covered under a piece of clothing, and the other man had a handgun on the ground at his feet, police said.
The officer immediately detained the men and called for assistance. When backup arrived, the men were taken into custody without further incident.
Police said the two men - 19-year-old Santa Rosa resident Manolo Iniguez Arechiga and 18-year-old Bernabe Ramirez Martinez of Boyes Hot Springs - are known gang members who frequent the Rockwell Place area.
Both men were arrested for possession of an illegal shotgun, possession of a concealed firearm, violation of probation and two gang-related enhancements, police said.
Arechiga and Martinez were booked into Sonoma County jail for the violations.
Anyone with information regarding this investigation is encouraged to contact the Santa Rosa Police Department's gang crimes team at (707) 543-3697.