What group of which almost half perished in the Sierras is Virginia Reed describing?

Virginia Reed is describing the Donner Party, a group of American pioneers who became trapped in the Sierra Nevada during the harsh winter of 1846-1847. Of the original group of 87 members, almost half perished due to starvation, harsh weather conditions, and other hardships. Their tragic story is one of the most infamous tales of westward migration in American history.