The U.S. Forest Service brought in additional resources on Sunday as the fire at Bridal Veil Falls continued to burn.

After strong winds enlarged the fire on Saturday, the Forest Service used a helicopter to dump water on the flames and airlifted a 20-person firefighting crew to the scene. On Sunday, two more helicopters were flown to the scene, including one known as the "sky crane," which can dump 1,500 gallons of water at once, according to Forest Service spokeswoman Loyal Clark.

The Forest Service also brought in a second 20-person crew to the scene for use in an area that would not be especially dangerous for firefighters, Clark said. The Forest Service declined to put firefighters on the ground on Friday, when the fire was confined to an abandoned restaurant, because it felt that the terrain and environment would have been too dangerous.

As of Sunday, the fire had not spread beyond the 40 acres that were burned on Saturday, but Clark said the blaze was not contained. Forest Service officials had no timetable for when they expected it to be contained.

There was also no additional word Sunday on the cause of the blaze. Clark said the Forest Service believed it to be human-caused, but were unsure whether it was set accidentally or by arson.

"The investigation is still continuing," Clark said.

The Provo Canyon highway -- U.S. 189 -- is still open, as are Vivian Park and Nunn's Park, but a trail between the two recreation areas is closed because helicopter rotors have been blowing large rocks down onto the area. The fire is not visible from the highway, Clark said.

The fire began late Thursday night in the abandoned Bridal Veil Falls restaurant. Shortly before the flames were extinguished on Friday, the fire started to spread to the outlying area, but Clark said they believed it would be contained by the following day.

But late Friday night, thunderstorms started to hit the area, and the resulting wind blew burning embers from the torched restaurant into the trees. More storms on Saturday did not bring enough rain to dampen the fire, Clark said, but the gusting wind helped spread the flames.

Early Sunday evening, Clark said there was little chance of the fire spreading, but if more thunderstorms hit the area then the winds could further enlarge the blaze.

"If we do have thunderstorms ... that come through with gusty winds, then yes, there is a potential for the fire to spread," Clark said.

• Jeremy Duda can be reached at 344-2561 or jduda@heraldextra.com.