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BOULDER, Colo. — Crews continued to monitor a wildfire that was threatening homes near the Boulder city limits Sunday night. The blaze was about 50 percent contained late Sunday.

The Red Cross, assisting people forced to leave their homes, set up a shelter on the city’s east side. The dry, warm and windy weather has created the perfect conditions for the fire in the foothills to grow rapidly.

Crews said the fire was about 60 acres in size. More than 250 firefighters from across the Denver metropolitan area raced to Boulder County as the wildfire grew in size early Sunday.

Viewer Steve Conney captured video of the flames at 3 a.m. Sunday.

The fire is burning near the Seven Hills subdivision near Sunshine Canyon.

“They’ve done a great job, and they’re coming in from all communities,” one evacuee said. “We’re really grateful for that.”

The fire, scorching an area popular for hiking, forced crews to evacuate 426 homes.

“[My mom] has been in the foothills of Boulder for 52 years,” said Meg Hendricks, who evacuated her mother. “We’ve done this before. However, it’s never an easy process.”

People in roughly 800 additional homes, in a pre-evacuation area, were put on notice to be prepared to leave at any moment.

The Hendricks family didn’t wait for an official order. They got their mom, who lives in the pre-evacuation area, out of harm’s way.

The Hendricks were not sure if their mother would be able to sleep at home on Sunday evening.

“I’ll wait and see if the fire is near us, out or partly out before I decide if I’m going to go back home,” Jan Hendricks said.

Residents forced to evacuate can go to the Boulder High School parking lot at 1604 Arapahoe Road.

Residents who need temporary shelter can go to the East Boulder Community Center at 5660 Sioux Drive. Dogs, cats and small animals are permitted to stay with their families at the evacuation center.

The Humane Society of Boulder Valley is providing temporary shelter for dogs, cats and small animals of people affected by the fire.

By air, the Colorado National Guard did its part with helicopters. Authorities said pilots plan to continue dropping water on Monday morning.

Ground crews, monitoring the area overnight, also plan to be battling more flames again on Monday. The weather is expected to be much the same on Monday, with dry, warm and windy conditions.

“I think everyone’s paying attention to the wind and knowing how quickly that can change,” a Boulder woman said.

So far, there are no reports of any damage to homes or other buildings. There are no reports of any injuries.

Many open space areas and trails in the area are closed.

“At 1:40 a.m., Boulder Regional Communications Center received a 911 call from a man who reported seeing flames visible on the side of the mountain near Sunshine Canyon and Timber Lane,” The Boulder Office of Emergency Management said in a statement. “Firefighters and deputies responded to the area and ordered residents to begin evacuating.”

Crews said firefighters have been pro-active by forming defensive lines around homes to prevent damage.

People in the mandatory evacuation area will not be allowed to go home Sunday evening. Most are staying with family, friends or at hotels, according to the American Red Cross.

Authorities said they are investigating the possibility the fire was caused by a human instead of a natural cause. Boulder County Sheriff’s Office officials said they plan to update evacuees and the press around 8 a.m. Monday.