DENVER – Four people died in a small plane crash Sunday in the foothills west of Boulder, the Federal Aviation Administration said Monday.

The crash sparked a small fire that was quickly contained in the forested area. The cause of the crash was unknown, according to the FAA’s preliminary report. FAA spokesman Steve Kulm did not provide more information about the crash.

A witness called in the crash at 9:41 a.m. Sunday morning when the plane crashed in a wooded area of Lefthand Canyon west of Denver near the college town of Boulder, said Boulder County Sheriff’s Office spokeswoman Carrie Haverfield. She said the fire and heat blocked responders from entering the plane until Monday.

The plane, a twin-engine Cessna T337G, took off with three passengers and the pilot, Haverfield said.

Aerial footage shot by Denver7 shows first responders weaving through charred trees at the crash site.

Peter Knudson, spokesperson for the National Transportation Safety Board, said that an investigator is arriving to the site Monday and will spend two to three days documenting the crash site. A report about the crash is expected in two to three weeks, he said.

The National Transportation and Safety Board investigator is coming from Wyoming, where two people died in a plane crash Thursday.