In 1862, with the ranks of the Union army swelled by more than 100,000 volunteers, the U.S. government believed it could now spare enough men to again occupy the Utah Territory. In addition, it was important to protect the overland mail route and telegraph lines along what later became known as the California Trail. Col. Patrick E. Connor marched into Utah with a regiment of California volunteers. His soldiers, of the 3rd California Infantry, constructed a small garrison just three miles (5 km) east of the Mormon stronghold of Salt Lake City. The post, named Camp Douglas for former Illinois presidential candidate and congressman Stephen A. Douglas, was officially established on October 26, 1862. Connor at once engaged in an acrimonious and bitter cold war with Brigham Young and the Mormon people, whom he accused of being disloyal and immoral. During the rest of the war, the fort served as the headquarters of the District of Utah in the Department of the Pacific.
The District of Utah was organized on August 1, covering the territories of Utah and Nevada, and Connor was appointed commanding officer. Besides the California units Connor led into the territory, the district was also defended by detachments from the 6th and 11th Ohio Cavalry, elements of the 4th U.S. Cavalry, and the 1st Nevada Cavalry Battalion.
Main article: Bear River massacre
The Shoshoni and other Native American tribal groups engaged in several small conflicts with incoming immigrant settlers in northern Utah and south-eastern Washington Territory (present day Idaho), particularly during the late 1850s and early 1860s. One incident in particular involving miners from Montana traveling through Cache Valley was enough to justify an expedition to investigate the situation further. Eager for combat, Connor marched his regiment 140 miles over the frozen winter landscape to deal with the Indians. On January 29, 1863, Connor's troops encountered the Shoshoni encampment along the Bear River. His men massacred the Indian encampment and then marched back to Utah.
Connor encouraged his men to explore the Utah region for mineral deposits, the discovery of which he believed would bring more non-Mormons into the territory, changing the balance of political power. His efforts were successful. His men discovered gold, silver, lead, and zinc deposits in Tooele County in 1864. As Connor hoped, miners began to flock to the territory. The Rush Valley Mining District was established by soldiers in the western Oquirrh Mountains and more than 100 claims were staked in the first year.