Awild black stallion with about 20 mares at his side rears his head and stares intently, his body stiff and alert, ears perked.

We rein our mounts and freeze in the saddle. For a few moments nothing stirs; it seems as if even the birds notice the encounter and settle to watch.

Suddenly the stallion makes a decision. With a great snort and a whinny he turns and races away, leading his mares in a whirl of dust and pounding hooves.

The morning encounter with wild horses is one of many on a two-day ride through the 5,000-acre Wild Horse Sanctuary in Northern California. But it is one of the most special moments, because once we dismount and sit quietly several yards from the edge of the watering hole, the stallion reconsiders his decision about us and returns. The mares follow. They wait until he decides it's safe to drink, then join him.

About 200 horses and 20 burros freely roam this wild, open land in Shingletown, Calif., about a three-hour drive north of Sacramento. Except for the foals born here, most of the wild horses have been rescued from dire circumstances. A nonprofit organization headed by 58-year-old Dianne Nelson provides them a natural home. Donations to keep the sanctuary going are subsidized by travelers like us, who sign on for two- or three-day riding trips -- on tame, well-trained horses -- through the sanctuary.

At stops along the ride, Nelson shares her knowledge and her love for the wild horses we've come to watch.

"I have the deepest admiration and respect for them," she says. "They're survivors. They're the resource the West grew up on." White settlers and Native Americans alike tamed many of the horses that first came to the American West on the ships of Spanish explorers beginning in the late 15th century. Over the centuries they mated with horses lost or released by the U.S. Cavalry, miners and ranchers.

"Their ancestors carried everyone around," says Nelson. "They brought the freight, the mail. They pulled the wagons and the plows. You name it, they did it."

The six guests who meet at Nelson's house on the edge of the sanctuary this Saturday morning in July range in age from 11 to 57. One New Jersey mother has brought her horse-loving daughter as a 13th birthday present. The girl is the only experienced rider. I ride every chance I get, which is a couple of hours about once or twice a year. I fear that at the end of a day of riding, someone will have to pry my feet from the stirrups and settle my bottom on a block of ice.

I'm assigned to Marco, a tall, regal gelding on permanent loan from a woman who didn't have time to ride him. Nelson's mount, Pathfinder, was a bottle-fed foal. The mother was a wild horse. When her colt was three days old, the mare approached Nelson's daughter and collapsed at her feet, dead of an infection.

"It's like the mother delivered her baby into my hands. I carried her home on my lap," says Nelson.

Three college interns volunteering at the sanctuary join us on the ride led by Nelson. Except for an occasional trot, the horses walk the tough, mountainous range where hardy purple, gold and white wildflowers manage to grow amid mounds of volcanic rock.

During the ride we climb 2,000 feet. All the while, in the distance, we can see the snowcapped Cascade Mountains, on the other side of which, beyond our line of sight, lies the Pacific Ocean. The only sign of civilization within views that stretch for miles: an occasional power line.

We're barely out of the paddock when a hare dashes across our path. A few minutes later a rattlesnake slithers in front of Nelson's horse, which remains calm and simply gives the snake wide berth. We see the bones of a colt; Nelson says a mountain lion that attacked two tame horses in her paddock probably killed it. The bones have been picked clean by turkey vultures, one of several raptors, including hawks and eagles, that share the sky over this land with 150 varieties of songbirds.

But we've come to see the wild horses and soon come upon a band of about 10 mares and a stallion. About half an hour later we spot two "bachelor" horses that hang out together. Only the strong get to mate, and the strongest take more than their fair share, gathering harems around them.

"They'll steal each others' mares if they get a chance," Nelson tells us. One burro apparently snuck into a harem one night. The mule that resulted from the affair was shunned by all the other horses. But the horses can also show great compassion, Nelson says. This spring, she tells us, she saw a harem without a stallion. Later, she found the stallion with a new colt and mare. He had apparently taken the risk of losing his harem by staying behind to help the baby and its mother.

We spot the black stallion and his band at the watering hole after several hours of riding under the hot sun. While our mounts rest and the mustangs warily keep their eye on us while drinking, we settle in the shade for lunch and talk.

"You can go to a Pony Express museum and see saddlebags and stirrups and such," says Nelson. "But the California mustang was the favorite mount of the Pony Express riders, and the progeny of those horses are still here. They're alive. I like to give people a feeling for that living history."

Nelson first came to know the wild horses in the early 1970s. She lived on remote Bureau of Land Management land for months and even years at a time, paid to catch wild horses the federal government considered excess. The land can support only a certain number of animals, and wild horses compete with range cattle raised by ranchers on federal land.

The horses Nelson caught back then were adopted out, until one year, when she was told that 80 mustangs no one wanted were going to be slaughtered. "I couldn't see that happen to these marvelous animals, so I said I'd take them." She kept them on ranchland lent by a supporter for a few years, until the BLM decided to replace her and use helicopter crews to round up mustangs they wanted to remove from federal land. Nelson was out of a job, and thus out of money for hay and grain for her charges.

With the encouragement of friends and other mustang supporters, Nelson called talk shows, newspapers and TV stations throughout California, seeking sponsors for her horses and decrying the slaughter of animals that symbolized American freedom and Western spirit, animals whose ancestors helped win the West.

Knowing she'd need more land to rescue more horses from slaughter, she sold everything she had and bought 60 acres in Shingletown. The sanctuary has since purchased more land and is leasing major tracts that are often in jeopardy of being sold, including a 2,000-acre parcel currently up for bid.

Congress eventually responded to the pleas of people like Nelson and, in 1982, instituted a moratorium on slaughtering wild horses. Still, wild horses in dire need keep coming Nelson's way. Sometimes, she hears reports of horses being hurt in the wild or abused. Sometimes, people who adopt horses from the BLM find they can't tame them, or don't want them after all.

(The BLM estimates that about 40,000 wild horses live among the 261 million acres overseen by the federal agency. Last year, the BLM rounded up 10,081 wild horses and burros, and was able to find homes for 5,891. The rest are penned in hopes of future adoption.)

Our ride through the sanctuary is not for sissies, especially not during the hot summer months. Much as I love pretending to be a cowgirl, after nearly six hours in the saddle I am insanely grateful to arrive at our overnight campground. Snacks and huge coolers of icy drinks await us, along with our sleeping bags and other luggage that has been trucked to the site.

Those with energy to spare help unsaddle and brush the horses, but most of us simply chat and await the sunset.

The staff prepares steaks and chicken over an open grill, and cornbread, potatoes and other hearty side dishes in the cookhouse. One of the interns plays the fiddle as we sit around the campfire that night.

I'm amazed that I've emerged from the long ride without bodily consequence. I did walk bowlegged for about half an hour after first arriving and have a few scratches from close encounters with trees, but the soreness I expected never arrives.

By morning, after a huge breakfast, I'm ready for the ride back to the ranch. Ready to experience a small remaining piece of the Old West, and a view of the wild horses that helped to tame it.

At the Wild Horse Sanctuary in Northern California, the horses run free -- you ride the tame ones.Wild Horse Sanctuary's Dianne Nelson (in hat and black top) leads riders through the Northern California preserve to see wild stallions and mares.Visitors ride through Wild Horse Sanctuary land by day, then camp at night.