photo - Lefthand Fire District Chief Steve Lynn walks back to get supplies as crews battle the Sunshine Fire in the Sunshine canyon area of Boulder, Colo. on Sunday, March 19, 2017. The small wildfire forced people from their homes early Sunday and ignited dead trees that exploded into black plumes of smoke, authorities and residents said. (Jeremy Papasso/Daily Camera via AP)
Lefthand Fire District Chief Steve Lynn walks back to get supplies as crews battle the Sunshine Fire in the Sunshine canyon area of Boulder, Colo. on Sunday, March 19, 2017. The small wildfire forced people from their homes early Sunday and ignited dead trees that exploded into black plumes of smoke, authorities and residents said. (Jeremy Papasso/Daily Camera via AP) 

BOULDER, Colo. (AP) — Hundreds of residents were allowed to return to their homes in the foothills just outside this university city on Monday as firefighters make progress against a wildfire possibly sparked by transient campers in the area.

The fire spread to about 70 acres, but firefighters fully contained it Monday afternoon by building lines to stop it from spreading. Winds were forecast to be a bit lighter than when the fire broke out on Sunday, helping crews mop up hot spots and control flare-ups overnight.

Boulder County Sheriff's Cmdr. Mike Wagner said the blaze may be human-caused and that hikers and transient campers frequent the area where it erupted — a wooded, mountainous place a couple of miles from Pearl Street, the shopping and dining hub in the heart of the home of University of Colorado. Officials ruled out any lightning strikes or downed power lines, and Wagner said investigators were working to pinpoint exactly where it started.

Last year another wildfire in the county was accidentally started by two men camping in the mountains who didn't fully put out their campfire. It destroyed eight homes near the small town of Nederland.

Resident Anne Shusterman said the vast majority of people camping around the area are those who chose to live without a home, not people who have fallen on hard times and have no other choice. She said she no longer feels safe running along trails because of them and worries about the fire danger posed by them in tinder-dry conditions.

"I don't know what it's going to take for this city to wake up," said Shusterman, who lives near the fire and woke up to find heavy smoke around her home Sunday.

The latest fire started in the Sunshine Canyon area, which is dotted with expensive homes and rustic mountain residences. Dead trees exploded and sent black smoke skyward.

Residents of 426 homes were ordered to evacuate and people who live in over 800 others were told to be ready to leave if conditions worsened.

Officials worried that stronger wind gusts could fan the flames overnight. Residents of 836 homes were told to be ready to leave if conditions worsened but high winds did not develop.

No structures have been damaged.

Although Colorado's mountain snowpack is healthy — ranging from 105 to 130 percent of normal on Monday — most of the state's eastern half, including the populated Front Range, is experiencing some degree of drought. Many local governments have enacted fire bans after weeks of warm, dry and often windy weather during what is normally one of the snowiest months of the year.

Wagner said conditions seemed more like what might normally be found in June rather than March.

Firefighter Jason Morley told the Daily Camera newspaper that the conditions on Sunday were brutal.

"I've never seen if like this before," he said. "There is no snow at all up there. If you picked up grass, it would just crumble in your hands."

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