The blaze, called the Mann Fire, started in the dry Santa Ana River bottom and was reported just before 10 a.m. near California Avenue and Grulla Court, according to Cal Fire Riverside.
The fire went on to threaten some 500 homes.
Officials said two people suffered non-life threatening injuries. Five properties also had minor damage to fencing and outbuildings.
Video from AIR7 HD showed flames approaching several hillside houses. Firefighters raced to protect the homes while helicopters performed water drops from overhead.
Evacuation orders were issued for the area north of North Drive, from Crestview Drive to California Avenue; and the area north of Eighth Street, east of Pedly Avenue and south of the Santa Ana River bottom, the agency said.
Evacuation centers were established at Corona High School, 1150 West 10th Street in Corona, and Jurupa Valley High School, 10551 Bellgrave Ave. in Jurupa Valley.
The cause of the fire is unknown.