The journey westward was highly dangerous for the early pioneers - conditions were harsh, and the distance was great. The story of the Donner Party highlights the plight and severeness of such a journey.
About 80 people, led by George Donner, set out from Missouri on a wagon train in May 1846, following the famous
trailblazer Lansford W Hastings.
The party left Fort Bridger, at the foot of the Rockies, on 31 July, which was late in the season.
They made the tragic decision to take the Hastings Cut-off - a shortcut which they were told would save them 400 miles.
The route was too hard. They had to abandon all their cattle while crossing the Salt Lake Desert. They were attacked by Paiute warriors. Fights broke out - in one, a man was killed.
On 30 October the party reached the last mountain pass before California, where they were stopped by snow - after a journey of 2,500 miles.
They were just 150 miles from Sutter's Fort, now Sacramento, in California.
For four months the party ate first their cattle, then bark and twigs. Finally some turned to cannibalism - eating parts of people who had already died. Many died of starvation.
Rescue groups from Fort Sutter managed to rescue the others - the last one only in April 1847. Of 87 who set out, 46 survived, and 41 died.