During the peak years of the California gold rush, an emigrant would have found it practically impossible to travel the trail in isolation. From the end of April, when the grass began to green up on the prairie, until September, when snow started to fall in the Rockies, bringing travel to a halt, an almost unbroken stream of wagons stretched out across the Great Plains.

Near South Pass, reported Franklin Langworthy in 1850, "The road, from morning till night, is crowded like Pearl Street or Broadway."

In 1852, John Kerns noted, "I believe I could count 5,000 wagons this evening in sight." In the same year another man reported that "he frequently passed solid processions of wagons three miles long—and often 3 wagons abreast."

Before the gold rush, the trail was not quite so crowded. For safety's sake, most emigrants banded together...