A chunk of the hill came down Sunday between Lambert and Plume ways -- sending boulders, mud and debris down onto the sidewalk below.
Homes up on the ridge were evacuated as a precaution, and will remain evacuated until a cause is determined and the damage is repaired.
One resident told ABC7 about 12 people in the area lost power.
"I lost power but it was kind of weird because I lost power in the front of my house and then the rest of my house shortly afterwards," said Stephanie Pfafman. "We lost power because the hill coming down took out the transformer at the bottom of the hill."
It's unclear whether recent heavy rains caused the slide or if there is another issue. Some people told Eyewitness News the hillside was very saturated.
"I worry about my neighbors who live close to this spot," said Santa Clarita resident Joey Yang. "It's quite shocking... I just don't want anything more serious to take place."
Building and safety officials were expected to respond to the neighborhood Monday to figure out what caused it.
"This plastic's been out here for weeks and they said they were dealing with erosion and it would be here until May and they were drilling a few weeks ago," said resident Rich Pepe. "It must've been related, but then all of a sudden, I guess with that little bit of rain that we had ... it was just enough to send it over the edge."
The housing development where it happened is relatively new.