The Platte River and Straight Creek fires that broke out Thursday have calmed down, with firefighters reaching 50% and 100% containment, officials said Sunday afternoon.

The Platte River Fire has burned 37 acres in Jefferson County, while the Straight Creek Fire has burned 8 acres east of Dillon.

Crews worked Saturday to address the fire lines surrounding the Platte River Fire and used a helicopter to drop water on hotspots, according to officials with the Pike and San Isabel National Forests. Most of the fire’s containment is north of County Road 97 and along the southern edge of the fire.

On Sunday, crews continued to work on the fire lines to halt the fire’s growth, with emphasis on patrolling, monitoring and holding the control efforts of the previous two days.

As the fire has calmed down, firefighters will begin to be released throughout the day. There were 34 firefighters on the scene as of Sunday morning, officials said. The blaze started on private land and burned onto U.S. Forest Service land, Jefferson County sheriff’s deputies said. It started in the Dome Rock/Ramona Gulch area, near the 17000 block of West Platte River Road, not far from Foxton and Buffalo Creek.

The cause of the fire remains under investigation. A downed power line might have started the fire, according to the county sheriff’s office.

The fire will not be fully contained for several weeks because of the extremely rugged terrain and the safety risks to firefighters, said officials with the Pike and San Isbel National Forests. During this time, crews will continue to patrol and monitor the fire.

Meanwhile, crews made fast progress on containing the Straight Creek Fire, with 50 firefighters working Saturday on strengthening containment lines and mopping up through the dead and down trees in the burn area, according to officials with the White River National Forest.

Two elite Forest Service “hot shot” crews remained on the fire through Sunday. Local crews will continue to monitor the Straight Creek Fire following the full containment.

The cause of the Straight Creek Fire is also under investigation, officials said.

The Forest Service has issued a closure for the area southeast of the fire for firefighter and public safety, including the Straight Creek Trail and Tenderfoot trail system.

As the state braces for another potentially busy wildfire season, residents are advised to use caution when building campfires, make sure they are completely out before leaving camp, be sure to keep trailers from dragging, and avoid parking in dry grass.