Crews have been spraying fire retardant on at-risk houses in the Tujunga suburb, and they have dug a 12-mile line in the scrub to stop the fire's progress.
A squadron of aircraft, including eight air tankers and 13 helicopters, have been deployed to bombard the blaze.
"I'm feeling a lot more optimistic today than I did yesterday," Mr Dietrich told journalists on Tuesday.
"The crews are doing fabulous work out there on the ground, but the bottom line is that they're fighting for every foot."
More than 10,000 residents have fled the flames, and some 6,600 homes are under mandatory evacuation orders.
California Governor Arnold Schwarzenegger declared a state of emergency and urged people to comply with evacuation orders. He paid tribute to the efforts of the emergency services, saying they were the "most well-trained, courageous firefighters in the world".
As well as co-ordinating the fight against the blaze, he said officials must now also help residents rebuild their lives.
Many people left everything behind as they fled, unsure whether there would be anything to return to.
Residents speak of their fears as the fire continue to spread
Bert Voorhees and his son salvaged several cases of wine they had left in their swimming pool for safekeeping - all they could manage before fleeing their home.
"You're going to be living in a lunar landscape for at least a couple of years, and these trees might not come back," the 53-year-old told the Associated Press.
"Are enough of our neighbours going to [come back and] rebuild?"
Wildfires are a feature of the Californian summer, but it is unusual for them to break out so close to major population centres.
The latest fire is not being fanned by the Santa Ana winds that typically kick up in October. Instead, it is being fuelled by extremely dry brush that has not burned in more than 40 years.
A number of other fires are also burning in southern and central California.
A blaze in Placer County, north-east of the state capital, Sacramento, has destroyed 60 structures, many of them homes in the town of Auburn.
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