To Americans 'the West' was an ever-changing concept. At the time of the first federal census in 1790, 95 per cent of America's four million people lived hard by the eastern seaboard and 'the West' was virtually everything else. By the 1820s, it extended not much beyond the Appalachians. Even as late as mid-century a chronicler like Charles Dickens could venture only as far as St Louis, still the better part of a thousand miles short of the Rockies, and plausibly claim to have seen the West.

The move to the West as we now know it began in earnest in the mid-1840s, when the expression 'Oregon fever' erupted. Encouraged by the government to settle the north-western territory claimed also by Britain, homesteaders set off in their thousands for a new life at the end of the Oregon Trail, following a route blazed by trappers 20 years before.

Oregon Trail is a somewhat misleading term. After the first few years relatively few of those who travelled the trail were heading for Oregon. Once past the Rockies, they instead broke off and made for the gold fields of California.

One of the great myths of the westward migration, compounded by a thousand movies, was that the immigrants lumbered over the prairies in Conestoga wagons. These sturdy vehicles were, in the words of the historian George R Stewart, 'uselessly heavy for the long pull to Oregon or California'. They did haul some freight west, but almost never did they transport families. Instead, westward immigrants used lighter, smaller and much nimbler wagons universally known as prairie schooners. These were hauled not by horses but by mules or oxen, which could withstand the hardships of prairie crossings far better than any horse could.

Another myth engendered by Hollywood was that wagons gathered in a circle when under attack by Indians. They didn't, for the simple reason that the process would have been so laborious to organise that the party would very probably have been slaughtered before the job was even a quarter accomplished.

Wagons were covered with canvas, as in the movies, though that word was seldom used; the material was more generally known in the 19th century as twill. Though 'wagon train' was also used (it is first recorded in 1849), the term wasn't particularly apt. For much of the journey the wagons fanned out into an advancing line up to 10 miles wide, to avoid each other's dust and the ruts of earlier travellers - providing yet another obstacle to their forming into circles.

Many of the early homesteaders had only the faintest idea of what they were letting themselves in for, and often through no fault of their own. Until well into the third decade of the 19th century ignorance of the West remained so profound that maps were frequently sprinkled with fanciful rivers - the Multnomah, the Los Mongos, the Buenaventura - and with a great inland sea called the Timpanogos. Those who went west, incidentally, didn't think of themselves as still being in America. Until about the time of the Civil War, 'America' was generally taken to signify the eastern states, so that accounts of the time commonly contain statements such as 'Some people here (in Oregon) are talking about going back to America' or 'We'll go back to America. Dressed up slick and fine' (from, respectively, the New York Tribune in 1857 and the Rocky Mountain News in 1860).

The traditional western stagecoach, notwithstanding its perennial role in movies and television programmes, saw active service for only a little over a decade. The first service was inaugurated in 1858, when the Overland Mail Company began twice-weekly trips from St Louis to San Francisco. Its Concord coaches (named for Concord, New Hampshire, where they were developed) were intended principally to carry mail and freight but also carried up to nine passengers at dollars 200 each for the westward trip and dollars 150 for the eastward. (Eastward was cheaper because the traffic was mainly one way, westward.) All being well, the trip took a little over three weeks. In 1866 the Overland Mail Company was sold to Wells, Fargo and Co, but it was put out of business by the opening of the first transcontinental railway three years later.

Even more short-lived was the Pony Express. Inaugurated on 3 April 1860, it was designed to carry mail as quickly as possible from St Joseph, Missouri, to Sacramento, California. Riders rode in relays, averaging 50 to 80 miles a day (though some occasionally went as far as 300 miles without a rest), carrying a mail pouch or mochila, as it was more normally called. On an average run, 75 riders would cover the 2,000 miles between Missouri and California in ten and a half days. It was a fabulous achievement, but economic folly. Setting up and maintaining riders, horses and way stations was an exceedingly costly business. By late 1861, barely 19 months after starting, the Pony Express was out of business, a victim of the newly installed telegraph and its own inescapable costs.

Altogether, getting to California was a dangerous and uncomfortable affair. But that didn't stop anyone - at least not after gold was found there in 1849. In the first four years of the gold rush, the population of California went from 20,000 to just under 225,000. In those same four years, dollars 220m in gold was pulled from the ground or sluiced from its glittering creeks.

The gold rush not only enriched a fortunate few, but enlivened the language. Many of the terms that arose from it soon made their way into more general usage, among them pay dirt, pan out, to stake a claim and to strike it rich.

One of the many side-effects of the gold rush was the invention of hard-wearing canvas trousers and bib overalls in San Francisco in the 1850s. The inventor was, of course, Levi Strauss, who had travelled west with a load of canvas (or twill) intending to make tents, but found a much greater demand for trousers that would stand up to the wear and tear of life in the mining camps. He didn't call them jeans. In the 1850s the word signified not an item of apparel but a type of cloth. It is a corruption of Genoa, the Italian city where it was first woven. Not until this century did denim (itself a corruption of serge de Nimes from the French city) trousers become generally known as jeans and not until the 1940s were people calling them Levis.

The traffic to California wasn't all from east to west. Many thousands came from China. At the beginning of the gold rush, just 325 Chinese lived in California; two years later the number had jumped to 25,000. In the next three decades it increased twelvefold to more than 300,000, or nearly one-tenth of the population. Because of political turmoil in China, almost all of them came from just six small districts in Guangdong province.

The Chinese, who for entirely mysterious reasons were commonly known in the West as 'Johnnies', were treated exceptionally badly. Because they were prepared to work hard for little pay, and because their appearance precluded easy assimilation, they were often pointlessly attacked and occasionally even massacred. Even banding together didn't provide much protection. In 1885, in Rock Springs, Wyoming, a mob swooped on a community of 500 Chinese for no reason other than that they didn't like them, and left 28 dead. Such was the prejudice against the Chinese that in some western courts they were not even permitted to plead self-defence. Thus there arose the telling western expression, 'He doesn't have a Chinaman's chance.'

Much of the inflated speech that seems such a natural accompaniment to the high-spirited lifestyle of the West - formations like absquatulate and rambunctious - had originated long before in New England. Likewise, the stetson hat, also often called a John B, was an eastern innovation. Its originator, John Batterson Stetson, was a Philadelphian who never intended the hat to be exclusively associated with guys on horses.

Even 'cowboy' was an old term. It was first used during the Revolutionary War as a disparaging epithet for loyalists. In its modern sense it dates from 1867, when an entrepreneur named Joseph McCoy (another oft-named candidate for the source of the expression 'the real McCoy') began employing cowboys to run longhorn cattle up the Chisholm Trail from Texas to his railhead at Abilene, Kansas. He became immensely successful, and by the early 1870s was shipping out up to 500,000 head of cattle a year from the dusty town. ('Cow town' didn't enter the language until 1885.)

Hollywood has left us with the impression that the West was peopled by little but cowboys. In fact, farmers outnumbered them by about a thousand to one. Even at their peak there were fewer than 10,000 working cowboys, at least a quarter of them black or Mexican (and the remainder not a great deal higher up the 19th-century social scale).

The cowboy of popular imagination was largely the invention of two highly unlikely easterners. The first was the artist Frederic Remington, whose action-filled, hyper-realist paintings were in fact largely studio creations based on a lively imagination. He never saw any real cowboys in action. For one thing he was immensely fat - much too fat to get on a horse, let alone ride it into the midst of Indian battles. Even more crucially, by the time he made his first trip to the West the cowboy age was all but over.

No less disconnected from life around the camp-fire was his close friend Owen Wister, who mythologised cowboys on paper in much the same way that Remington mythologised them on canvas. Cowboys had begun to appear as heroes in dime novels as early as the 1880s (the genre appears to have been the invention of one Prentiss Ingraham), but it wasn't until Wister published The Virginian in 1901 that the cowboy (or cow-boy as Wister insisted on spelling it) truly became a national figure.

Wister was the quintessential dude. Scion of a wealthy Philadelphia family and grandson of the celebrated actress Fanny Kemble, he was a Phi Beta Kappa at Harvard, a close friend of Teddy Roosevelt, and of a decidedly delicate disposition. Unlike Remington, he actually travelled in the West, though he hardly hit the dusty trail. He was sent west by his parents to recover from a nervous breakdown and was chaperoned throughout by two spinsters.

Although Wister introduced many of the conventions of cowboy fiction - the use of a hero without a name, the introduction of a climactic shoot-out between the hero and villain, the immortal line 'When you call me that, smile]' - his main achievement was to make the cowboy a respectable figure for fictionalisation. He began the process with a now forgotten novel called Lin McLean, but brought it to full fruition with The Virginian. The story of an easterner (unnamed, of course) who goes west, it struck a chord with millions of Americans, but particularly among the better educated at whom it was aimed. The book sold 50,000 copies in its first four months and 3 million copies overall, went through 15 printings in its first seven years, and was made into a Broadway play that ran for 10 years, and subsequently into a seminal film.

The mythologising of the West was consolidated in the immensely popular novels of writers like C J Mulford, creator of the absurdly uncowboylike Hopalong Cassidy, and Zane Grey, a New York dentist who knew almost nothing of the West but refused to let that get in the way of a good tale.

The first movie western, The Great Train Robbery, came in 1903. By the 1920s, westerns accounted for nearly a third of all Hollywood features. But their real peak came in the 1950s on television. During their zenith year, 1959, the American television viewer could choose among 28 western series running on network television - an average of four a night.

It is decidedly odd that these figures of the West, whose lives consisted mostly of herding cows across lonely plains and whose idea of ultimate excitement was a bath and a shave and a night on the town in a place like Abilene, should have exerted such a grip on the popular imagination.

Cowboys certainly didn't spend a lot of time shooting each other. In the 10 years that Dodge City was the biggest, rowdiest cow town in the world, only 34 people were buried in the infamous Boot Hill Cemetery, and almost all of them had died of natural causes. Incidents like the shoot-out at the OK Corral, or the murder of Wild Bill Hickock, became famous by dint of their being so unusual.

Those who were shot seldom got up again. Scarcely a western movie has been made in which at least one character hasn't taken a bullet in the thigh or shoulder but shrugged it off with a manly wince and continued firing. In fact, 19th-century bullets were so slow, relatively speaking, and so soft that they almost never moved cleanly through the victim's body. Instead, they bounced around like a pinball and exited through a hole like that created by a fist punched through paper. Even if a bullet miraculously missed the victim's vital organs, he would almost invariably suffer deep and incapacitating shock and bleed to death within minutes.

Justice was often peremptory and swift - thieves and cheats on riverboats were generally put down on the nearest sand-bar and left to make their way back to civilisation, if they could - but at least justice there was. Land-based miscreants were often dealt with by 'kangaroo courts'. This rather odd and interesting term has been traced to Texas, a place notably deficient in antipodean marsupials, and was first recorded in 1849. It appears to have no connection to Australia - the expression was unknown there until introduced from America - and may derive from the idea of a criminal being bounced like a kangaroo to the gallows, but that is no more than conjecture.

Extracted from 'Made in America', to be published by Secker and Warburg on 4 July, pounds 15 hardback.

1994 by Bill Bryson.

Readers of the 'Independent' can order copies of 'Made in America' at the special price of pounds 10, postage and packing free, by sending a cheque to Reed Book Services Ltd, PO Box 5, Rushden, Northants NN10 6YX, or by phoning the Credit Card Hotline on 0933 410511. Please quote reference 111514.