The Donner Party was a group of American pioneers who set out for California in 1846. They became trapped in the Sierra Nevada mountains during the winter due to heavy snowfall. The party consisted of several families and individuals, totaling about 87 members. As supplies dwindled and conditions worsened, some members resorted to extreme measures for survival. Only 48 of the original group survived to reach California in the spring of 1847. The tragic story of the Donner Party highlights the challenges faced by westward travelers during the California Gold Rush.