 What is now Clark County was acquired by the United States during the Mexican–American War, becoming part of the northwestern corner of New Mexico Territory.In 1847, Jefferson Hunt and other Mormon Battalion members returning to Salt Lake City from Los Angeles pioneered a wagon route through the County that became the Mormon Road.In 1849, this road became known as the "Southern Route", the winter route of the California Trail from Salt Lake City to Los Angeles during the California Gold Rush.