The Los Angeles County Sheriff's Department says two people were shot around 1:45 p.m. Sunday near Muscatel Avenue and Longden Avenue, in an unincorporated part of San Gabriel.
Both victims underwent surgery at a local hospital and were listed in critical condition.
Officials say the suspect taken into custody was Adrian Ness, 80.
The alleged victims are his 90-year-old wife and his 54-year-old son.
Ness was being held on $2 million bail.
The motive for the shooting remains under investigation.