UNNATURAL WONDER; HOOVER DAM, WHICH ENERGIZED LAS VEGAS -- LITERALLY -- RANKS AS A CONSTRUCTION MARVEL OF THE 20TH CENTURY.

Byline: Eric Noland Travel Editor

Taming the natural world.

It was practically a compulsion of man's at the start of this century. A canal was carved through the then-mosquito-infested swamps at the Isthmus of Panama and completed in 1914. The Holland Tunnel, more than 1-1/2 miles in length, was burrowed beneath New York's Hudson River in 1927. The Empire State Building climbed to an unthinkable height of 102 stories in that city four years later. Two bridge projects were begun across belligerent San Francisco Bay in the early 1930s.

But the feat widely regarded as the most remarkable of that era is Hoover Dam, a wedge of concrete jammed into the Colorado River over a Godforsaken canyon on the Nevada-Arizona border. Even now, more than a half-century after its completion, it remains an object of fascination, attracting more than a million visitors annually.

They peer over the 726-foot face of the dam or take a tour through the bowels of the power plant, where water is forced through steel pipes as wide as 13 feet in diameter and 560-ton rotors turn in gargantuan generators.

If they linger long enough to hear the human stories behind its construction, visitors learn that Hoover Dam is more than an impressive feat of engineering. It is an enduring tribute to the individual workers who labored through backbreaking tasks in torturous conditions to get it built. Most had little alternative; the Depression directly coincided with the dam project, and anyone who griped or faltered could be (and often was) replaced in a snap.

Imagine what had to be accomplished with 1930s technology: In often-searing desert heat, four diversion tunnels, 56 feet in diameter and averaging more than 4,000 feet in length, were hacked and blasted through the rock walls of the canyon. Dump trucks poured hundreds of loads of rocks into the Colorado River to create a temporary dam and force the river into the tunnels. The riverbed was scooped out, down to bedrock some 75 feet below. Finally, concrete was poured into a maze of wood forms - tons of concrete, enough to build a two-lane road from Los Angeles to Boston.

The dam, a National Historic Landmark administered by the U.S. Department of the Interior, is an easy excursion for visitors to Las Vegas - it's a 31-mile drive southeast via U.S. 93. Hoover Dam is a worthy diversion if only because it was solely responsible for putting the glitter in the gulch.

Las Vegas was nothing more than a dusty, bawdy frontier town of 5,000 when the dam contract was awarded. It quickly swelled with laborers and their families, and later embraced workers seeking unrestrained recreation. When the dam was completed and the power switches flipped on, there was ample juice for the neon that would follow.

An impressive visitors center was erected at Hoover Dam four years ago, complete with a new, roomy elevator that descends 50 stories through the canyon wall to the power plant. A hard-hat tour was added a year later, supplementing a standard tour that has been popular for years.

The 30-minute standard tour, which costs $8 for adults, leads visitors - in groups of up to 60 - to the power plant at the base of the dam, onto a balcony that overlooks the eight generators on the Nevada side of the plant, out onto a ramp that provides a view up the mammoth face of the dam, and into a tunnel where a viewing platform takes in one of the enormous penstock pipes through which water is fed to the generators from Lake Mead.

For $25, the hour-long hard-hat tour is limited to 16 or so visitors and navigates the warren of tunnels and walkways deep in the dam's heart. (You get to keep the hat.) Unless you're an engineering buff or profoundly curious about this operation, you can probably dispense with this tour; you'll find the standard tour to be perfectly adequate. Dam officials also advise people who suffer from claustrophobia to steer away from the hard-hat tour.

On a recent visit, the hard-hat excursion was conducted by Bruce Laughlin, a brusque, burly sort who wears aviator sunglasses indoors and whose protective headgear is a hard-plastic cowboy hat. At several stops, he held forth on the intricacies of hydroelectric power generation, and while a few in the group seemed to grasp the concepts, the rest of us were content simply to gaze around. (Gee, that's a really big bolt.)

The tour also provided perhaps the tiniest inkling of what the working environment might have been like. Black Canyon was chosen as the site of the dam because at that point the Colorado cut through a narrow cleft in the rocks. Today, at the base of the dam, the dark, rocky walls rise steeply on both sides, blotting out any shred of a breeze and funneling the oppressive desert sunlight onto this spot as if with a magnifying glass.

Just walking across the outdoor ramp causes beads of sweat to sprout beneath the free hats. Now imagine what it would be like to wield a jackhammer or shovel in these conditions for eight hours.

Laughlin was not without a sense of humor. At one point, he led the group through a pipelike air shaft near the top of the dam. One by one, we approached a metal grate and took in a dizzying view of the Colorado River far below. ``Try not to lean on the grate,'' the guide said from the darkness behind us. ``We don't know if it's on real tight.''

Several tidbits of information were dispensed. On this blowtorch of a day in early September, we were told, demand for power would run high when Southern California's air conditioners started coming on in the early afternoon. ``We'll be running all 17 generators at full power later today,'' Laughlin said.

He also talked of the El Nino year of 1983, when the Colorado River was swollen ominously by runoff from the Rocky Mountains. The waters of Lake Mead rose to within seven feet of the top of the dam, and the spillway had to be activated. (Farther upriver, Glen Canyon Dam's diversion tunnel linings were severely damaged, but Hoover Dam's half-century-old construction barely flinched.)

Laughlin also addressed the two most-asked questions by visitors to Hoover Dam: How many people died building it, and how many workers are entombed in it?

The answer to the latter query is none. The dam was built in a series of interlocking blocks and columns - if a continuous pour of concrete had been used, the core would have risen in temperature as it was hardening, and the concrete would have taken 125 years to cool. Thus, when a load of concrete was dumped into each form, it spread out and was never deeper than six inches.

This is not to say there was not a burial fatality, though. According to Joseph E. Stevens' excellent book, ``Hoover Dam: An American Adventure,'' (University of Oklahoma Press; $17.95), a wooden form gave way during one pour and a worker was swept off a scaffold in an avalanche of wet concrete. His body was dug out 16 hours later.

The total number of fatalities in Hoover Dam's construction is a subject of debate. One popular item of lore records the first death as J.G. Tierney, a Bureau of Reclamation employee who fell from a barge and drowned in the Colorado River during a geological survey of prospective dam sites in 1922. It records the last victim - No. 112 - as Patrick Tierney, an electrician's helper who fell from one of the intake towers back of the dam in 1935. Patrick was J.G.'s son.

But this coincidence is almost too convenient - to make it work, you have to ignore a death on an earlier survey mission.

A more reliable figure is 96 - the recorded number of industrial fatalities on the construction job itself. Most were the result of falls, according to Laughlin.

It's a wonder there aren't more today, with the top of the dam crawling with tourists on a daily basis. If you suffer from acrophobia, a look over the 4-foot wall at the top of the dam's face will turn your knees to gelatin. The words ``Please Keep Off Wall'' are stenciled into the concrete at regular intervals, which can mean only one thing: People have been known to climb up there to pose for pictures.

Inside, out of the heat, the Hoover Dam visitors center provides numerous opportunities to learn about not only the engineering particulars but also of the human stories of the construction. (For those who opt not to take tours, admission to the visitors center alone is $4 for adults.)

One of the best features here is tucked away in a theater on the exhibit level. It is a 60-minute documentary film created by the Public Broadcasting System as part of its ``The American Experience'' series. Every visitor should block out an hour to watch this in its entirety.

The film includes priceless black-and-white footage of the dam's construction, plus a glimpse at the plight of family members who lived out of cars, in cardboard hovels at a riverside camp called Ragtown, and later in the sterility of the company town that was built for the workers, Boulder City.

There are also present-day interviews with men who worked on the dam. One such fellow says grimly, ``There were three shifts a day, every day, with two days off a year - the Fourth of July and Christmas . . . optional.''

For the consortium of six contractors that was entrusted with building the dam, the timing of the project couldn't have been any better. The federal government authorized the project exactly 17 months after the stock market crash of 1929.

In the days before ``safety net'' referred to social policy, people were desperate for work. They descended on this barren corner of the Mojave Desert by the hundreds, and created a vast waiting list at the dam's hiring office. Six Companies, led by superintendent of construction Frank T. Crowe, exploited this buyer's market odiously.

Early on, there were deaths by heat prostration because water wasn't made available at remote reaches of the job site, even at times when temperatures climbed into the 130s. (One unconscious man transported to a Las Vegas hospital registered a temperature of 112 degrees.)

During the excavation of the diversion tunnels, men suffered acute carbon monoxide poisoning because Crowe insisted on using gasoline-powered trucks to haul out the rubble, in open defiance of Nevada mining law. Six Companies faced stiff federal fines for missing various construction-phase deadlines, and Crowe - who earned the nickname ``Hurry Up'' among the workers - was loath to endure the delay (much less the expense) that would be required to convert the trucks to electric motors.

The contractors maintained a hospital in Boulder City, but the Hippocratic oath took a severe beating there. Men stricken with gas poisoning were routinely diagnosed as having pneumonia or influenza, even when they died from the poison. Stevens reported in his book that near the completion of the dam, when one worker died after suffering a head injury in a fall, the cause of death was listed as spinal meningitis - a non-job-related malady, and thus not subject to compensation.

Early in the project, a brief, ill-fated strike was waged. It's reported that most of the workers relented simply out of hunger - Six Companies provided a free mess hall for men on the job.

Not surprisingly, ``Hurry Up'' Crowe brought the job in early - more than two years ahead of schedule. And Hoover Dam, which threw an immobilizing harness over the Colorado River, was to have an immediate and profound impact on the West.

The Imperial Valley, which had suffered through disastrous floods early in the century - including one that formed the Salton Sea - blossomed as a newly fertile agricultural area. Los Angeles, a small town with a perpetual thirst, grew in direct proportion to the water and power it received, first as a military aircraft production site during World War II, later as a thriving aerospace center.

And Las Vegas . . . well, in the town that moderation forgot, growth was accelerated on two prongs: the legalization of gambling in Nevada in 1931 and the gusher of electricity that began to flow out of the dam's power plant five years later.

Today, Hoover Dam has numerous cousins along the Colorado (Glen Canyon, Parker, Davis dams), and Los Angeles and Las Vegas have nearly outgrown it. Hard-hat tour-guide Laughlin noted that while 56 percent of Hoover Dam's power goes to Southern California, that represents only about 1 percent of what the region uses. And the dam accounts for only about 4 percent of the power that Las Vegas requires.

Where does the remainder come from? Coal-fired and nuclear plants.

It all began here, though.

It began soon after then-Secretary of the Interior Harold Ickes stood up at the dam's dedication ceremony and said, ``Pridefully, man acclaims his conquest of nature.''

At the start of this century, it was an important boast.

IF YOU GO

GETTING THERE: Hoover Dam is a 31-mile drive southeast of the Las Vegas Strip, requiring 45 minutes in moderate traffic. From the Strip, head east on any of the major thoroughfares (Tropicana, Flamingo, Desert Inn, etc.) to U.S. 93/95 and go south. When the highway splits, follow U.S. 93 to Boulder City. Once in Boulder City, signs to the dam will try to direct you on a crawl through the town's business district. To avoid this, turn left at Buchanan Boulevard - which doubles as U.S. 93 Truck Route - and proceed to the dam.

HOURS: The visitors center is open from 8 a.m. to 5:45 p.m., with the last tour conducted at 5:15 p.m.

COSTS: Admission to the visitors center for those electing not to take a tour is $4 for adults, $2 for kids ages 6 to 9. The half-hour standard tour is $8 for adults ages 17 to 61, $7 for seniors age 62 and up, $2 for kids ages 6 to 16. The hour-long hard-hat tour costs $25. Parking in the dam's multiple structure is $2.

INFORMATION: For general information on visiting Hoover Dam, phone [phone]. Web: www.hooverdam.com.

CAPTION(S):

5 photos

Photo: (1 -- 2) A visitor, left, peers over the 726-foot face of Hoover Dam. The dam, built in the 1930s, is considered one of the most remarkable engineering feats of the 20th century. Above, tour guide Bruce Laughlin leads visitors along a ramp outside Hoover Dam's power plant, a vantage point that provides stunning views of the dam's face and the steep canyon walls alongside it.

(3) A hard-hat tour of Hoover Dam includes intriguing features such as this cylindrical air shaft near the top of the dam. The view of the Colorado River out the grate at the far end causes knees to wobble.

(4 -- color) Tours of Hoover Dam offer a look at the enormous generators of the power plant.

Eric Noland/Travel Editor

(5 -- color) Hoover Dam presented a challenge to engineers in the 1930s. The had to jam a wedge of concrete into a narrow desert canyon.

Laine Scheilga/Knight Ridder/Tribune Photo Service