The first-responders went to the home at about 12:55 p.m. after receiving reports that a resident had been injured when he stepped on something. Within an hour, deputies had the property cordoned off while they conducted their investigation.
A neighbor told NBCSanDiego that the blinds in her house were rattled by the explosion.
"There was a loud explosion, and it shook my windows," said neighbor Lauranell Latulippe.
Latulippe said she went outside afterward, but, since she didn't see any smoke or hear any screaming, went and picked up her kids at school. She said the explosion was very loud, similar to the the noise made when a transformer blows up.
Sheriff's department spokeswoman Jan Caldwell said the homeowner was doing some sort of landscaping when some sort of explosive devce detonated, injuring the man doing yardwork.
"The homeowner had a couple of people working in the back yard, doing some landscaping or work in the yard, and one of them reports stepping on something, and then, right after that, there was a blast," Caldwell said. "Injuries were consistent with some sort of explosive device. Injuries are on the left side of the person's body."
Deputies said the injured man was taken to a Palomar Medical Center with cuts and lacerations. His injuries are not believed to be life-threatening.
Deputies plan on sending a robot into the back yard to clear it and make sure it's safe before entering the site to investigate the scene. She said the scene to "go on for a while today."