Two trucks were damaged by fire overnight at the Tehama County Sheriff's Search & Rescue yard.
The fire was reported at 12:05 a.m. at 2010 Park Avenue. One of the vehicles involved was a heavy military surplus truck and the other was a semi-truck without a trailer.
Firefighters said crews knocked the fires down quickly, and there was not extension to other vehicles or the Tehama County Search and Rescue building nearby.
City fire units remained on scene for more than two hours to assist investigators and to overhaul the burned vehicles.
Red Bluff Fire Chief Jon Bennett said the fire is suspicious but the cause is undetermined. The investigation is being handled by Cal Fire and the Tehama County Sheriff's Office.