Antelope Island » Twelve miles of rugged terrain now behind them, a small army of volunteer wranglers has pushed a heard of bison within sight of the pen. At the 23rd annual Great Bison Roundup, the day's work is nearly done.

But now there's a standoff. The herd won't budge. The bulls have started fighting back. Two horses have been gored. Most of the rest of are exhausted from the push.

At the top of a rocky precipice, overlooking the row, Marcia Wolkerstorfer leans back on her saddle and rubs a hand through a tuft of brown hair on her steed, Bandit.

Her grin is wide.

The Minnesota woman might seem to be an unlikely warrior in this fight. At 60, she knows there are safer and easier pursuits. "My kids think I'm totally off my blooming rocker," she said.

But ever since her children left home, Wolkerstorfer has had an insatiable desire for adventure. She has driven race cars at 130 mph. She has helped protect endangered sea turtles on the island of St. Croix. And four years ago, she found herself helping to move 650 horses to their winter pasture in Colorado.

So the moment she read about this annual rite, in the entertainment section of her newspaper, she knew she had to be here.

"I got right on the phone and said, 'sign me up,' " Wolkerstorfer said.

She arrived in Salt Lake City on Friday morning. And Saturday morning she was behind the Antelope Island herd, helping to push the enormous, growling beasts from the southern tip of the island, in the middle of the Great Salt Lake, to the corrals on the northern end. Over the next few weeks, veterinarians and state park personnel will weigh, vaccinate and conduct various health tests on each bison to determine the herd's health. Then, to keep the herd size at a level that the island can sustain, about 200 head will be sold at a public auction. Money generated by the sale goes into the Antelope Island wildlife management program.

Driving bison isn't as easy as moving cattle. That's one of the reasons so many volunteers are needed. But park officials don't have to ask for help. Each year, hundreds of volunteers arrive from across the country.

Jeff Daugherty started volunteering when he was planning and development director for Salt Lake County. A few years ago, Daugherty took a job in Teton County, Wyo. But he still returns to the roundup every year.

"It's never the same," Daugherty said. "It's always different friends. The weather is different. The challenges are different. The adventure is different. But it's always amazing."

Mike Brown, a wrangler at R&G Horse and Wagon Co., which outfits dozens of volunteers for the roundup each year, said the annual event isn't for everyone.

"The people who do this, they have to have a brave spirit," he said.

mlaplante@sltrib.com