Fierce wildfires erupted in Southern California on Monday, leaving two people dead and heralding the start of the most intense period of the fire season here. The most severe fires, fanned by stiff, dry Santa Ana winds typical of the fall, were burning several thousand acres at the rim of the San Fernando Valley. A homeless man and his dog died when fire engulfed the wood-and-cardboard shack where they lived along a freeway embankment, and another person died in a collision on a freeway on-ramp attributed at least in part to thick smoke shrouding the area. With strong winds expected into Tuesday, firefighters mounted an all-out air and land assault as the flames and smoke chased residents from their homes, threatened neighborhoods, closed schools and parts of two major freeways, and led Gov. Arnold Schwarzenegger to declare a state of emergency in Los Angeles and Ventura Counties.