The house is located on the 22500 block of Pico Street in Grand Terrace. Officials said a 57-year-old man living there is in custody and is expected to be booked on attempted murder charges.
Investigators said he became irritated with a man who was picking up his grandchild from the day care center next door.
A fight broke out and the suspect was allegedly subdued before he could pull the trigger of his gun.
Deputies found around 15 assault rifles in the house, along with numerous handguns, shotguns and ammunition.