Investigators looking into a fire that destroyed 15 boats at a remote marina in Glen Canyon National Recreation Area haven't identified a cause of the blaze that generated $3-$5 million in damage to boats and dock facilities.

The fire erupted late Thursday night at the Halls Crossing Marina. It took firefighters until about 3 a.m. Friday to douse the blaze.

While officials originally thought 20 boats were destroyed by the flames, on Monday they revised that total downward to 15. Of those, three vessels sank, at least one of them in water 200 feet deep.

NRA officials say there were 153 watercraft docked at the marina, which is about 95 river miles up Lake Powell from Glen Canyon Dam. The fire destroyed the marina’s “F” dock, charring boat slips and melting part of the roof covering the dock. A few other boats sustained minor damage, but most were saved by the quick actions of those who first responded to the fire, including National Park Service and marina concessions staff and other volunteers.

An initial assessment estimated the value of the loss of boats and facilities at between $3 million and $5 million, said Max King, Glen Canyon spokesman and acting public affairs officer. The remains of those boats and some of the others have been moved to a secure area for examination by investigators from the Utah State Fire Marshal’s office and the U.S. Bureau of Alcohol, Tobacco and Firearms, which is assisting because the fire was at a federal facility.

The remains of “F” dock, one of six sets of docks at the marina, are cordoned off and not open to boats or the public. The portion of “D” dock containing boat slips numbered 11 and higher also is off-limits, according to the marina concessioner, by order of the fire investigators. Ranger King said that prohibition includes all individuals, slip holders and insurance company representatives.

The NRA spokesman said that in their initial examination of the fire scene, investigators found no evidence that the fire was deliberately set. The Utah fire marshal continues to categorize the fire’s cause as unknown.

“Indications are that it's going to take some time to find the cause,” Ranger King said, noting that the “marine environment” of the fire will make determining its origins more complicated. He added that investigators have left the scene for now but will return after the first of the year to continue their work.

The marina is in one of the more remote locales of the recreation area, which encompasses more than 1.25 million acres in southern Utah and northern Arizona along the course of the Colorado River.

“As we move into the investigation phase, the role of the National Park Service is shifting to assistance as needed and securing the scene,” Ranger King said.

Scott Ryan, chief ranger at Natural Bridges National Monument about 60 miles from Halls Crossing, has begun to assess the site for any potential environmental damage so that appropriate clean-up measures can take place.

Anyone with information about the fire or needing to contact investigators should do so through the Utah State Fire Marshal’s office. The phone number is 801-284-6350.