The wheelchairs nosed up a slope, volunteers nudging them around holes and rocks.

Brad Childs had gathered his hikers in a circle to explain that some of the upcoming trails were going to be a little difficult, that they’d have to stick together, and that they might see eagles, vultures, woodpeckers, squirrels and other Santa Monica Mountains fauna.

“And turtles, right?” said a little pigtailed blonde, a note of authority in her voice.

Very authoritative indeed for a 4 1/2-year-old.

“Well, yes, Heather, maybe turtles too,” Childs answered.

“Heather Ann,” she corrected him.

Heather was the youngest of the group that had gathered for a hike into Cheeseboro Canyon on the edge of Agoura Hills. Age and very short legs were her handicap, but many of the other hikers had bigger handicaps. Six of them were in wheelchairs, including her father, Paul Flora of Sylmar.

Several times a year, the Wilderness Institute of Woodland Hills organizes hikes for the handicapped. About 25 people, including five guides from the institute, gathered at the head of the trail as the sun began to climb toward a very warm Sunday.

Thirty-one miles away in downtown Los Angeles, 18,861 runners had begun challenging the 26.2-mile course of the Los Angeles Marathon. For the participants in the institute’s hike, two or three miles and back on a dirt mountain trail was challenge enough.

“I’m a city boy. I don’t know much about the outdoors,” said Sid Luther, 34, a Glendale auto mechanic. “But I really like the chance to get out on a hike at a pace I can do.”

Luther has Frederick’s ataxia, a neurological disease that impairs his sense of balance, but he hikes with the help of a long walking stick.

“I put a real good charge on the batteries last night,” said John Payne of Ventura, who has an electrically powered wheelchair. He hasn’t walked since the Fourth of July, 1980, when he dived into a swimming pool and broke his neck.

Many of the participants had taken part in the Wilderness Institute’s “wheels to the sea” outing in November, a five-mile trip through Sycamore Canyon to the beach at Point Mugu.

“I thoroughly enjoyed that, and I wanted to do it again,” Payne said. “Being in a group like this takes away the worry of getting stuck someplace.”

“We’ll have some challenges, where the group will have to bond together,” said Childs, executive director of the institute and a former National Park Service ranger. “The challenges are part of the fun.”

The group set off about 50 yards behind 15 Sierra Club members, who went first so the guides wouldn’t have to talk over each other.

Childs pointed out a valley oak riddled with thimble-sized holes.

“Those were made by acorn woodpeckers. They peck the holes and store acorns in them to feed on later, either the acorns or the insect larvae that grow in the acorns. The hole always fits the acorn just perfectly. Nobody has ever figured out whether the woodpeckers make the hole to fit a certain acorn, or make the hole first and then pick an acorn that fits it.”

He pointed out a vulture drifting on a distant thermal. “You can tell vultures from other birds of prey because they hold their wings up in a V.”

Heather was far ahead, small running shoes flashing at a dogtrot, and was about to lap the Sierra Clubbers.

“Heather, what are you doing up there?” Childs called. “Are you scouting the way for us? Wait up.”

“Heather Ann , “ she replied, speeding up her pace.

Childs caught her and took one of her hands. She grabbed his other hand, flipped over in a somersault and took off down the trail.

Her mother, Carol, who has cerebral palsy that makes speaking difficult, made annoyed hand signals for her to return.

“Whoops, I’m going to crash,” said her father, Paul, whose wheelchair had suddenly started to veer down an embankment.

Two institute volunteers held him in the chair while another eased it back to the path.

Electric motors whirring, the wheelchairs nosed up a slope, volunteers nudging them around holes and rocks.

“There was a guy on another hike whose chair petered out right in the middle of a stream,” recalled Tina Johann of Woodland Hills, a recreational therapist at a home for delinquent boys who does volunteer work for the institute on weekends.

“We all helped him get back.”

Pointing out a patch of layered sandstone, Childs lectured on how the mountains evolved from what had been the ocean floor millions of years ago. “Even on the highest peak in the Santa Monicas, you can find fossilized seashells,” he noted.

Childs’ wife, Bonnie, also a National Park ranger who works only part time now (“One day a week, riding horse patrol in my Smokey Bear hat”), pointed out how wild mustard, introduced by the Spaniards, displaces native plants.

Rangers conduct controlled burns to destroy the invader, she said, pointing to a steep hill covered with mustard.

Heather waved back from the peak.

Hand signals from her mother brought her scrambling and sliding down to join the group for a rest and water break in the shade of a grove of oaks.

“OK,” Childs said a few minutes later. “We’ll go about another mile and stop for lunch.”

Away down the trail they went, Luther stalking deliberately onward with the aid of his stick, the wheelchair motors grinding.

Flora’s chair worked a little harder than before. Heather had crawled into his lap and gone to sleep.

Oops. Heather Ann .