Coal mining has changed a lot since the first half of the 20th century, when most of the nation's miners were underpaid, worked in dark underground holes and were subjected to explosions, cave-ins, deadly gases and black-lung disease.

Today, the majority of the nation's miners work above ground,

Once coal is mined, it's hauled to processing facilities where it is crushed, treated and mixed according to customer's specifications. Almost all of the coal from the Powder River Basin is used to fuel power plants.

are protected by stringent federal safety standards, and are well paid, compared to laborers in other fields.

The average Black Thunder miner, for example, works four 12-hour shifts on successive days and then has four days off. He earns $51,000 a year.

Many of the 570 mine employees at Black Thunder live in hotel rooms or trailers in nearby Wright for their four-day shifts and commute to their homes in Gillette 40 miles north, or to their hometowns even further away, when their work week is over.

Removing coal from the fossilized swamps of the Cambrian age is a three-step process.

First, the topsoil is scraped away with bulldozers and carefully set aside to be replaced after the coal is removed.

"It's treated like gold," plant superintendent Paul Barber said of the topsoil.

Coal industry advocates point out that only eight of Wyoming's 90,000 square miles have been disturbed by surface mining.

But before the mid-1900s there were few regulations dictating what coal companies had to do with the land once the fuel was removed. So many of them did nothing, simply packing up their equipment once the mine went dry, leaving behind deep, jagged scars.

In 1977 Congress passed legislation mandating the reclamation of mined property. Today, the Arch Co. is required to post a $200 million bond for every acre it mines as a promise that the land will be returned as close to its original state as possible after the coal is gone. Lange said his company has about 14,000 acres of government-owned land under lease for Black Thunder, but predicts less than half of that will be mined during the next 20 years.

Once the topsoil has been removed, crane-like machines called draglines lift the soil, or overburden, away from the coal seams.

The draglines are the biggest and most expensive of the mammoth machines used in the mining process. The largest of the machines, which cost about $60 million to build, is 50 stories tall at its spire-like top and can chomp 300 tons of dirt and rock in one bite.

When the coal is exposed, explosives are used to blast it out of the earth. From there it is loaded into trucks the size of barns that can haul three train carloads worth of coal, or about 340 tons, in one trip.

Then the coal is crushed according to the size specification of the customer and deposited in unit trains that haul it directly to the power plant.

To prevent coal dust and residue in highly populated areas, customers can ask the coal company to spray a latex sealant over each train car.

Trains creep through the Black Thunder plant two at a time, 10 to 12 a day, as they're filled.

The wholesale price of coal, $4.70 to $5 a ton, is so low compared to other fossil fuels that producers such as Arch have to produce enormous volume, up to 5.5 million tons a month, to stay profitable. Mines operate 24 hours a day, 365 days a week to maintain the thin 4 percent profit margin that keeps them in business, Lange says.

A shutdown would mean financial disaster, so producers duplicate their equipment and production lines and keep their own maintenance and emergency equipment and crews on site. Black Thunder mine hasn't closed since a mammoth blizzard socked it shut in 1986.

"It looks simple," Barber said of the surface mining process. "But when it gets down to the details, it's really not so simple."