In December 1845, the editor of the New York Morning News proclaimed that it was the "manifest destiny" of the United States to "overspread and possess the whole of the continent". It is hard for us now to realise how far that destiny then was from fulfilment. Within three years, Texas and the present states of California, Arizona, New Mexico and Colorado would have been captured from Mexico in a blitzkrieg. Oregon was still British territory, the remotest fief of the Hudson's Bay Company. In the whole of what is now two-thirds of the land area of the United States, outside Texas, the Mountain West was still the home of Native Americans, together with a sprinkling of missionaries and a few hundred fur-trapping "mountain men".
Only after gold was found in California, in 1848, did mass migration begin. In the next 12 years, 300,000 people migrated to California, to Oregon and to the Mormon city of latter-day saints in Utah. But before the Gold Rush, fewer than 20,000 altogether travelled west overland. They were for the most part the middling sort of people. The rich did not need to emigrate from the US. The poor could not afford to - because you needed money to equip yourself with flour, bacon, coffee and sugar, a wagon and draft animals, and to pay guides and Indians.
Frank McLynn has done justice to the courage and the endurance of those who did take the Oregon and California trails. In heavy wagons, mostly pulled by slow, long-suffering oxen, they crossed the plains from Missouri by the Platte River valley, risking flash floods. They moved on through the foothills of the Rockies, in southern Wyoming, to cross the continental divide at South Pass. At Fort Bridger, the trails divided, north by the Snake and Columbia Rivers to the fertile Willamette Valley in Oregon, and south-west across the fearsome salt deserts of northern Nevada and through the sierra to California. On these northern trails, unlike the Santa Fe trail, ruled by the sadistic Comanches, there was little danger from Indians. McLynn calculates that the mortality rate among the migrants was 4 per cent - and only 4 per cent of those were killed by Indians. In fact, the overlanders killed more Indians (426) than the Indians killed of them (362). Diseases such as cholera and "Rocky Mountain fever" were far more lethal. A handful were killed by grizzlies, bison or wolves. Rattlesnakes were terrifying, but killed more mules than people. Swarms of mosquitoes so dense they could choke you if they entered your mouth were more of a threat.
In those pioneer years, all the emigrants lived close to disaster, but only one party fell into the heart of darkness. Tempted by an adventurer to try an unproven "cut-off" across the Nevada Desert in 1846, the Donner party reached the sierra exhausted, short of provisions, and so late that their way was blocked by heavy snowfalls. Near where modern Californians drive up to Lake Tahoe and their weekend cottages, half the party came to horrible ends, as cannibals and their victims. They killed each other for their money and their body parts. Relief parties found human organs stewing in iron pots, and a baby clinging to the body of his butchered mother.
The Mormons, following a similar path in the same year to the Zion in Utah which they called Deseret, survived, thanks to the charismatic leadership and discipline of Brigham Young, although not without biblical tribulations of their own.
McLynn has combed the vast secondary literature on every aspect of the journeys. What is surprising is how many primary sources there are, too, preserved in diaries and other accounts written at the time, or in recollection afterwards. There is even a diary written by one of the ill-fated Donner party, as well as a passable poem, recalling an idyllic English village childhood, by another man dying of starvation. The word epic is overused, but the story McLynn has told, and told well, deserves it.
Godfrey Hodgson has just completed a book about America over the past 25 years