BOISE, Idaho -

Blaine County Sheriff officials say a central Idaho wildfire that caused 20 homes to be evacuated was started by an 18-year-old man lighting fireworks on private property.

The sheriff's office says no charges have been filed but an investigation is ongoing. The office has not yet released the man's name.

Officials say the teenager confessed to causing the 728-acre Colorado Gulch Fire --which started last Sunday-- after investigators found fireworks where the blaze first sparked.

The U.S. Bureau of Land Management is also investigating the fire because the flames spread to public land.

Fire officials say the Colorado Gulch Fire is expected to be fully contained Wednesday evening and completely snuffed out by Friday.