MIDDLETOWN, Calif. — As firefighters battled a massive Northern California wild land blaze threatening numerous homes, some of the 13,000 people urged to flee their residences were spending what may be just one of many nights in evacuation shelters.

The blaze that has charred nearly 97 square miles of brush and timber, jumped a highway Monday that had served as a containment line. Its rapid growth caught firefighters off guard and shocked residents.

Vicki Estrella, who has lived in the area for 22 years, stayed at a Red Cross shelter at Middletown High School along with her husband and their dog.

“It’s amazing the way that thing spread,” Estrella said. “There was smoke 300 feet in the air.”

Cooler weather had helped crews build a buffer between the wildfire and some of the thousands of homes it threatened as it tore through drought-withered brush in Lake County that hadn’t burned in years.

But Monday afternoon erratic wind blew hot embers north of Highway 20 ignited several fires across the highway north of the city of Clear Lake.

“There were too many (spot fires) for us to pick up,” Battalion Chief Carl Schwettmann of the California Department of Forestry and Fire Protection told the San Francisco Chronicle. “With these drought-stricken fuels, it’s just moving at an extremely high rate of speed.”

At least two dozen homes have been destroyed over the past few days and more than 13,000 people forced from their homes or warned to leave.

The fire — the largest blaze in drought-stricken California — roughly tripled in size over the weekend, generating its own winds that fanned the flames and reduced thousands of acres of manzanita shrubs and other brush to barren land in hours.

“There’s a lot of old growth-type vegetation and four years of drought to dry it all out,” said Lynne Tolmachoff, a spokeswoman for the California Department of Forestry and Fire Protection. “It was ready to go.”