A welder's torch apparently sparked the Garza fire near Garza and Withers roads at about 2:30 p.m. on Monday. Authorities have not been able to locate the person responsible.
Winds pushed flames toward a cluster of homes, forcing evacuations. They have since been lifted.
More than 125 acres of brush have been charred including parts of an ecological preserve.
Thirty-one engine crews and six inmate hand crews -- numbering around 200 people - worked to contain the blaze, with the aid of three water- dropping helicopters and three fire retardant-dropping air tankers.
Anyone with information about the fire was urged to call the Riverside County Arson Hotline at (800) 633-2836.
City News Service contributed to this report,