They will gather Sunday along the railroad tracks southeast of Greeley, and they will close their eyes and remember 20 children who died in Colorado's worst traffic disaster.

And then they will dedicate a 21/2-ton granite spire that will forever mark the place where a high-speed train collided with school bus on Dec. 14, 1961.

Some of them will be parents who buried those children. Some of them will be brothers, and sisters. And some of them will be survivors of the accident, men and women who got out of the mangled school bus alive.

For Tim Geisick, it will mean the culmination of efforts that began months ago, when he read "The Crossing," a series in the Rocky Mountain News that chronicled the accident and its long-term effects for the families touched by the tragedy.

That accident had affected his family on both sides, and he decided earlier this year to spearhead the drive for a permanent memorial.

That effort will be realized at 11 a.m. Sunday, when the monument is formally dedicated.

When he looks ahead to Sunday, he knows it will be a relief, "that it's finally there for the kids."

Dec. 14, 1961, was a bitterly cold Thursday morning — the temperature stood at 6 degrees — when bus driver Duane Harms started out on his route in the Auburn farming community. He had no idea that the Union Pacific's City of Denver streamliner was running an hour and 45 minutes behind schedule.

Just before 8 a.m., with 36 children on the bus, Harms pulled up to an angled railroad crossing, where he had to twist around and look behind him for a train coming from the east.

Frost and condensation fogged the bus windows, the early morning sun hung low in the eastern sky, and a row of utility poles obscured his view. Harms never saw the train, which was moving at 79 mph, and pulled across the tracks.

He was almost clear when the lead locomotive caught the last few feet of the bus, ripping it into two pieces.

In a matter of seconds, 20 children were dead. They included five sets of siblings and cousins from several families.

Harms and 16 children survived, some seriously hurt, others with little more than bumps and bruises.

A little more than a year later, a county work crew ripped out the old crossing and realigned the road. Motorists no longer had to cross the tracks at the spot.

And although East Memorial Elementary School, which opened in 1963, was named to remember the children who died, nothing ever marked the scene of the accident.

From time to time in the past few years, Geisick thought about the accident, and the effect on his family. It bothered him that there was nothing where it happened to remember the children.

Geisick wasn't yet born in 1961, but the accident had been a presence in his life as far back as he could remember. A cousin, Randy Geisick, was on the bus and came away almost unscathed. But Mark and Kathy Brantner, who both died, were his mother's younger brother and sister.

The past few days have been a whirlwind as he's rushed to make sure every detail is taken care of.

And he's had tremendous help from many people.

"Everybody keeps volunteering to do stuff, and I just really appreciate it," he said.