Windsor, Colo. ? Natural gas leaks and the threat of explosions kept hundreds of anxious residents from assessing the damage to their homes on Friday, a day after a large tornado tore through a 35-mile stretch of northern Colorado, killing one person and injuring dozens.

The twister skipped through several towns in Weld County on Thursday, damaging or destroying homes, businesses, dairies and farms. The storm system pelted the region with golf ball-size hail, swept vehicles off roads and tipped 15 rail cars off the tracks in Windsor, a farm town about 70 miles north of Denver.

Police and more than 100 National Guard troops cordoned off a particularly hard-hit area of about one square mile on Friday so utility crews could check each home for gas leaks, repair gas mains severed by uprooted trees, remove downed power lines and clear streets of shattered glass and debris.

It might take a day or more to secure the area, said Bill Easterling, commander of the emergency response team.

“I think at this point it’s pretty much hit me,” said a dejected Cindy Miller, a 46-year-old high school teacher. “I’m not going home for a while.”

Before being ordered out Thursday, Miller found a wall to her house torn apart and insulation, glass, water and debris everywhere. Wooden planks had penetrated a bathroom wall, and her trampoline was in a neighbor’s yard.

Authorities said about 100 homes were destroyed and another 100 were damaged by the tornado, which began near Platteville, about 20 miles south of Windsor.

A 52-year-old man was killed at a campground near Greeley, said Weld County Deputy Coroner Chris Robillard.

Thirteen people were treated at hospitals, and more than 100 others received medical attention for minor injuries, said Jim Shires, a spokesman for emergency responders. Crews searched the cordoned-off area of Windsor and found no additional victims.

Gov. Bill Ritter toured the damage and declared state of emergency for the area.

“I think it’s just miraculous that there has not been more loss of life,” Rep. Marilyn Musgrave said after touring damaged neighborhoods Friday. She and Colorado Sen. Wayne Allard asked President Bush to declare the area a disaster to free up federal aid.

Conditions converged in just the right way, time and place to produce “a pretty remarkable tornado,” said Greg Carbin of the National Oceanic and Atmospheric Administration’s Storm Prediction Center in Norman, Okla.

Carbin, the agency’s warning coordination meteorologist, said he thought the tornado was likely packing winds of 110 mph to 135 mph. He said its wind speed can be determined by evaluating the damage.

Similar conditions were forming Friday, although Carbin said there seemed to be less moisture and the boundary between the cool and warm air was farther to the east.

Severe storms, some including tornadoes, also ripped through parts of Wyoming, Kansas, Oklahoma and California on Thursday, damaging homes and farm lands. In northwestern Oklahoma, a truck ran off a road that had been washed away by heavy rain, killing a 14-year-old boy, state troopers said Friday.

About 100 people have died in U.S. twisters so far this year, the worst toll in a decade, according to the weather service, and the danger has not passed yet. Tornado season typically peaks in the spring and early summer, then again in the late fall.