By Keith Coffman
DENVER (Reuters) - Three wildfires sparked by lightning raged out of control in rugged Colorado mountain terrain on Friday, prompting the evacuation of two towns and menacing a third.
The West Fork Fire Complex - consisting of two separate fires in Rio Grande County in southern Colorado - forced 600 residents of South Fork to flee as high winds helped the blazes grow from 12,000 acres to 30,000 acres overnight.
"The fire behavior we saw yesterday was so extreme, it was ... unprecedented," said Eric Norton, a fire behavior analyst with the National Incident Management Organization.
A smoke plume from the blazes billowed 30,000 feet into the air, and firefighters reported 100-foot (30-meter) flames.
A string of fires have claimed at least two lives, charred hundreds of square miles and torched hundreds of homes across the western United States and in Alaska, which is baking in a heat wave.
The blazes, coming just as firefighters near Colorado Springs have contained the state's most destructive wildfire on record, underscore concerns that prolonged drought conditions in the West could intensify this year's fire season.
Much of Colorado is on high fire alert for the next several days due to heat, low humidity and strong winds, the National Weather Service said.
Fire spokeswoman Betsy Coffee said firefighters were deployed around South Fork to prevent flames from entering the community. Aerial crews were attacking the blazes with fire retardant and water drops.
Farther east in Huerfano County, a wind-driven blaze forced the evacuation of about 800 residents of the town of La Veta. The fire was bearing down on Walsenburg, a community of 3,000.
Another Huerfano County fire that forced about 200 people to flee a Boy Scout camp this week has grown to 9,100 acres and destroyed nine structures and four outbuildings, fire officials said.
In Arizona, officials said more than 600 firefighters continued to make progress against a blaze that forced the evacuation of 465 homes near the city of Prescott, about 100 miles north of Phoenix. No structures have been lost.
The Arizona fire, which is 10 percent contained, has claimed 6,732 acres of bone-dry chaparral and pine forests since it broke out on Tuesday.
(Editing by Cynthia Johnston and Xavier Briand)