A lightning-sparked wildfire in rugged central Arizona (search) has grown to nearly 173,000 acres and residents in at least three communities surrounded by pine forest fear they could be in harm's way.

The blaze was burning about 20 miles southwest of the mountain communities of Pine and Strawberry — 12 miles from the point when evacuations there may be necessary.

By Wednesday night, the fire was also less than 6 miles west of Black Canyon City (search), a community of about 4,500 residents north of Phoenix, but wasn't considered an imminent threat to structures there.

On the eastern flank, firefighters worked to stop flames from jumping over the Verde River. Authorities were concerned that if it crossed the river, it could push into a canyon and race into Pine and Strawberry, which are just three miles apart and have fewer than 5,000 year-round residents.

The fire hadn't crossed the river by Wednesday night but concern remained since the ponderosa pine forest surrounding the towns has been hard hit by tree-killing beetles in recent years, said Vinnie Picard, another fire spokesman.

Picard said the threat of wildfires is something residents of Pine and Strawberry, located about 100 miles northeast of Phoenix, are getting used to having around.

"This is an issue they seem to be dealing with a lot up there," Picard said. "But it's hard to stay calm, cool and collected when the sky is filled with smoke and they have ash covering their property."

In her weekly briefing with reporters, Gov. Janet Napolitano (search) said the blaze "remains the most worrisome fire that we've got in the state right now."

More than 200 residents packed a Black Canyon City park Wednesday night to hear from fire officials about efforts to stop the blaze from reaching their community. Similar town hall meetings were held in Pine and Strawberry to discuss the fire and necessary precautions.

"We do have to be prepared, but there's no reason for panic," said Strawberry inn owner Cheryl Holland.

The blaze began June 21 as two lightning-started fires and destroyed 11 homes near Cave Creek, just north of Phoenix. The fire may have dealt a fatal blow to the world's largest saguaro cactus, which could be two centuries old.

The 46-foot Grand One, recognized in the National Register of Big Trees for its height, mass of limbs and a base circumference of nearly 8 feet, was scorched.

"As much as I'd like to be optimistic, I'm not," said Tonto National Forest spokeswoman Emily Garber about the saguaro's survival.

The National Interagency Fire Center (search) said Wednesday that 22 active large fires had burned across more than 905,000 acres in Alaska, Arizona, Colorado, Nevada, New Mexico and Utah.

In Nevada, good weather and an increased firefighting force helped slow huge wildfires burning in a vast area of southern Nevada. The total fire zone covers approximately 500,000 acres.

In Utah, relieved residents of the southwest community of New Harmony — nearly consumed by a 12,000-acre wildfire — have returned to their homes.

"God was looking out for us. Our property was unharmed," said Emily Jones, whose home was within 50 feet of the fire.

Officials Wednesday said they were most concerned about a 4,300-acre wildfire burning in the Desert Red Cliff Preserve about 10 miles north of St. George. The fire is burning in the prime location for habitat and native grasses for the endangered desert tortoise.