Carl Nolte, Chronicle Staff Writer

It is stone masonry in the sky, and the role model here is the Greek builder Archimedes, who said, "Give me a place to stand, and I will move the earth."

A trail crew living and working in the Yosemite backcountry is rebuilding a terrifyingly steep granite stairway, moving rocks the size of computer terminals on the shoulder of Half Dome in Yosemite.

The crew -- five men and a trail boss -- work on slopes with sheer drops of thousands of feet on either side.

Since June their job has been to rebuild the last half-mile of the spectacular Half Dome trail. To do it, they are replacing or rebuilding more than 400 rock steps just below the steel cables that lead to the top of the granite monolith, which is 8,842 feet above sea level and 4,000 feet above the floor of Yosemite Valley.

"This is not rocket science," said Brian Ward, the foreman or crew boss.

It is science nonetheless. The 21st century trail crew uses winches, levers,

rollers and muscle -- the techniques that built the Pyramids.

There are no architectural drawings to guide them. The work is done relying on judgment and experience. Ward and Greg Torres, two of the top rock- layers in the business, make the calls.

FAMOUSLY DIFFICULT TRAIL
The Greeks built temples and forts atop hills in their rockbound country, but there was nothing like the glacier-carved cliffs of Yosemite in the ancient world; there is nothing like the smooth, glistening rock of Half Dome anywhere -- the foot trail up the peak is famous for its difficulty.

The crew on Half Dome, National Park Service employees, were hand-picked for this job, which is scheduled to be completed by the end of September. "This is the first time I've worked on a trail like this," said John Ray, 44, who has worked on Yosemite trails for 13 seasons. He's seen most of the park and a lot of the 800 miles of back country trails. This one is different.

"It is all rock on rock," he said. By that he meant there is no soil and no cement to hold the trail together. "It is pretty challenging to me."

Ray helped rebuild the steep Mist Trail on the cliffs at Vernal and Nevada falls, where thousands of people climb thousands of steps cut into the rock.

442 STEPS

That's only the first stage of the 8.2-mile trip from the valley floor to Half Dome. The difference is that once out of the fir and pine forest, the trail leads steeper and steeper from the timberline up an exposed granite shoulder on 442 steps to the base of the dome itself.

This piece of rock has no official name; the crew calls it "the Sub Dome." Here is where the steep steps begin, straight up with nothing but air on either side. Beyond the steps is a small saddle and then 600 yards of sheer slope. To climb the last leg, hikers must pull themselves up by hanging onto steel cables.

The Half Dome trip is a famous hike, the next best thing to rock climbing. On a typical summer Saturday, 1,000 people make it to the top of Half Dome. Many others turn back, gasping in the thin air. Others are terrified by the sheer slopes and can't go on.

But enough hikers have made the trip since the trail up Half Dome was opened in the 1870s that it has become worn and dangerous. This spring, the nonprofit Yosemite Fund put up $110,000 to rebuild the trail.

It was just in time.

Some of the steps and the carefully built up switchbacks, which connect sections of the steps, were no longer well-anchored and could have let go.

INJURY POTENTIAL
"They were not tied into anything," said Ward, the crew boss.

"The trail had the potential to be dangerous," Ray said carefully. "The potential was there for someone to get injured."

The potential also always exists that the crew could get hurt, moving hundreds of pounds of rock up and down the steep slopes, walking on the slick rock in most any weather.

One slip, and . . . Well, they don't like to think of that.

The tools alone could ruin their day. They manhandle 18-pound crowbars -- trail bars they call them -- sledge hammers, a gasoline-powered jackhammer that weighs 70 pounds, a kind of winch called a grip hoist and chisels. It is dangerous work.

The crew works four 10-hour days, Monday through Thursday. The trail is closed from 7 a.m. to 4 p.m. those days, open the rest of the time.

FEAR OF THUNDERSTORMS
The summer thunderstorms that roll up over the Sierra crest are the biggest fear -- lightning strikes can be fatal. "Weather moves fast up here," said Ward, "and if it comes up, it runs us off the mountain."

Every day the crew commutes to work from their base camp -- a woodsy home away from home just off the John Muir Trail on Sunrise Creek, about two miles from the work site.

The men, lean and fit as wolves, can make the trip in 45 minutes.

The base camp -- "Camp Many Bears" they call it -- is the province of Merlyn Storm, who is the cook and camp boss. Storm, who helped set up the camp in early June, has been outside only twice this summer.

One of the escapes, she said, was a 20-mile, round-trip day hike to the snack bar at Glacier Point to get an ice cream.

FAMOUS CAMP FOOD
Trail camps are famous for their food, and this one does not disappoint. Storm, who grew up on a ranch in Montana, serves up meat and potatoes, salad, applesauce, free advice and classical music for dinner. There is an ample breakfast, and crew members pack their own lunches. Supplies come in by mule train once a week; the mules also bring propane for the cook stoves and the Sunday paper. They haul out garbage and recycling.

The camp is well named. Despite the steel storage boxes in the cook tent, bears patrol through most every night. "I can tell what they are thinking," Storm said. " 'Maybe somebody left out a sandwich.' "

It's a good life, if you don't mind hard work and living in the mountains for months at a time. Most of the trail crew workers learned their skills with the California Conservation Corps. A few, like 22-year-old Zeb Marjanovich, are high school dropouts.

"I needed a job," he said, "I was going nowhere. I got into the Corps, then this and here I am. I found love."

E-mail Carl Nolte at cnolte@sfchronicle.com.