FORT COLLINS – The gate is open, at last, and 10 bison that have spent the past 11 days in a wooden corral the size of a high school gymnasium are free to leave.

But they’re not moving.

Ten charter bus-loads of spectators stand a hundred yards back behind a yellow rope in Larimer County’s Soapstone Prairie Natural Area, a healthy breeze whipping hair in their faces and setting the knee-high grass aquiver. All eyes are on the herd of genetically pure bison, a scientific marvel six years in the making and the first of its kind in Colorado.

Yards away from a 1,000-acre prairie like the ones their ancestors roamed before the species tumbled to the brink of extinction, the Laramie Foothills Conservation Herd is not yet ready to run.

“This is kind of our mini-Yellowstone, so to speak,” said Mark Sears, standing before a crowd of 500 and gesturing toward the corral just minutes before the release.

Sears, Fort Collins’ natural areas program manager, was referring to the herd’s genetic origins in the Yellowstone National Park plains bison herd, which numbers more than 3,500 and is easily the largest in the world.

But bringing a bit of Yellowstone to northern Colorado was easier said than done: Brucellosis, a contagious disease that causes cattle to abort, is ubiquitous among the Wyoming herd and has tempered the resurgence of genetically pure bison. Today, most of the 500,000 remaining bison in the U.S. and Canada have at least some domestic cow DNA because of interbreeding.

So Colorado State University researchers worked with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service to scrub Yellowstone semen and embryos of brucellosis, creating genetically pure, disease-free bison.

People gathered first at CSU’s foothills campus and then at Soapstone last Sunday – National Bison Day – to celebrate that complex tango of genetic engineering and get a closer look at the animals as they explored their new home.

Native American tribesmen donning feathered headdresses sang songs to welcome the bison back to the grass plains and told attendees of the meaning behind their return.

Bison were a mainstay for many Native tribes, which hunted the animals and honored them for their utility and grace.

And Native peoples have traveled a similar path to that of the bison, said Ernest House Jr., executive director of the Colorado Commission of Indian Affairs and a member of southwestern Colorado’s Southern Ute Indian tribe.

Once prolific, both groups diminished in size with the advent of the American Pioneer age. Only 325 bison remained in the U.S. by the 1880s, down from more than 30 million in the 16th century.

“Today is a good day,” House said at the CSU celebration. “I feel good. And I know that our ancestors feel good for what’s going on today. Bringing these majestic animals back to this community fills a void in a lot of Native American cultures.”

It was a good day for Dr. Jennifer Barfield, too.

The CSU reproductive physiologist and lead scientist for the project saw “a dream being realized” as she entered the corral with three other key players.

The bison will become a seed herd for future growth of the species. A few of the nine females will give birth come spring, and the male calf will return to CSU in a couple of years to father still more bison.

Barfield entered the corral first as the rest of the group – USDA wildlife biologist Matt McCollum, Crow Nation Veterans Affairs Director Solomon Little Owl and USDA wildlife pathologist Jack Rhyan – followed closely behind.

They approached the gate in the pen’s southwest corner, eying with caution the herd of bison huddled on the north end. The bison stood with their dark noses pressed to the ground, shaggy winter fur rising like snowbanks up the steep humps on their backs, silky summer fur cloaking their surprisingly delicate hooves.

Then, as Barfield and the others came closer, the bison began to run. Not toward the gate, but away from it, then toward it again, then away, in a halting formation.

The group came still closer, waving their arms at the bison that stood once again frozen halfway to the gate.

And then, finally, they were off, galloping past the open gate and into the sun-drenched prairie in a flickering diamond shape like birds make in the sky.

On the sidelines, 14-year Larimer County Natural Resources employee Linda Wilson felt a lump rise in her throat. She and the rest of the onlookers watched as the bison disappeared into the horizon, soon barely visible amid the grass and hills and purple mountain shadows.

“It’s what they’re born to do, isn’t it?”