Two people heading inside a restaurant near the explosion were injured by the debris.
Southern California Edison workers continued to survey the damage and repair efforts Monday night.
"The first engine company that arrived found a sizable crater with two individuals down," said San Bernardino Fire Capt. Ben Alexander. "An underground power transformer had exploded. The vault had come through the street and caused the debris to fly and that's what struck the individuals that were injured."
The two people hurt were taken to a local hospital with minor injuries.
Investigators said it could have been a lot worse had the DMV across the street been open and the usual dozens of people were lined up on the sidewalk.
It was the second accident involving SCE in four days.
Just last week, three members of a San Bernardino family were killed after coming in contact with a high-voltage power line that fell in their back yard.
On Monday night, some nearby homes and businesses were without power.
"We have crews that are de-energizing lines, so power will be out for a short period of time," said Beverly Powell of SCE.