Fire officials have ordered mandatory evacuations for residents of 65 homes near a wildfire burning near a scenic canyon in northern Colorado.

The area evacuated Thursday is where residents had previously been warned to be ready to leave at a moment's notice, said fire information officer Kristy Wumkes.

The fire has grown from 1,000 acres to 5,000 acres in the last day as erratic wind gusts of up to 50 mph moved into the area fueled by thunderstorms that didn't produce rain. Another so-called dry thunderstorm is moving in Thursday.

Steep, rocky terrain and lack of roads in the area are hampering firefighting efforts. The terrain is dotted with dry ponderosa pine trees, grass and shrubs. The fire is burning north of the Cache La Poudre River that runs through Poudre Canyon. The area has seen little rain in recent weeks as drought conditions have left Colorado's snowpack at 11 percent of its 30 year average.

Three firefighters suffered minor injuries, including one who lost his footing and tumbled into some embers, Wumkes said.

"Think of double-diamond ski runs, that's how steep it is," Wumkes said.

All three firefighters have been treated and are back on the fire line, she said.

About 400 firefighters have been dispatched to the fire, and a heavy air tanker capable of dropping up to 2,100 gallons of fire retardant is assigned to the fire, along with helicopters that are capable of dropping hundreds of gallons of water are at the scene. Two more heavy tanker airplanes and a large helicopter have been requested.

Early Thursday, a thick smoky cloud settled over Fort Collins some 20 miles away from the blaze, prompting state health officials to warn that school children and people with lung or heart problems should stay indoors. A haze extended 65 miles south to Denver prompting concerns that it would affect planes at Denver International Airport, but officials there said operations had not been affected.

A cold front could bring cooler temperatures and higher humidity early Friday, said National Weather Service meteorologist Scott Entrekin.

Temperatures Saturday will be in the 50s and the humidity will be 40 to 50 percent, Entrekin said. The humidity was only 15 to 20 percent Thursday, which created prime conditions for the wildfire.

Elsewhere in the West, wildfires in New Mexico and Arizona are expected to leave a haze of smoke above both states.

Meteorologists say the concentration of smoke will not be near the level created by last year's wildfires, some of the largest in the history of each state.