Early years, mining, military service
Monihon was born to James and Ann (Martin) Monaghan, Irish immigrants, in Oneida County, New York on November 6, 1837.:236 When he was two, his family moved to St. Lawrence County where he grew up on a farm and attended local schools. Monihon joined the California Gold Rush in 1854, traveling by sea via the Isthmus of Panama.:447 After reaching San Francisco, California, he became involved in placer mining often around Howland Flat, Sierra County until 1861.:236
At the beginning of the Civil War, Monihon enlisted in Company F of the 1st California Infantry Regiment. While in the military, he served throughout the area that composes modern day Arizona and New Mexico. As Chief of the Howitzer division he fired a celebratory salute in Tucson on July 4, 1862.:447 Ten days later he saw action during the Battle of Apache Pass when his unit of 64 soldiers was attacked by over 450 Apache Indians led by chief Cochise.:236
Following the battle, his unit spent two months in Mesilla before being redeployed to Fort Craig.:236 In late 1863, Monihon's unit was ordered to Fort Wingate. From there they continued to the Chino valley where they established Fort Whipple.:448 Monihon served as Provost Sergeant at his new posting until his discharge at the end of the war.
He remained in central Arizona, where he worked in mining again for several years and ran a livery stable in Prescott. Much of his mining work was as engineer of the mill at the Big Bug mine. In 1868, Monihon sold the livery business, the Plaza Feed and Livery Stable, to Gideon Brooke and Jacob Linn.
George M. Willing tried to sell him half ownership in the fraudulent Peralta land grant for $250 in 1867. Willing suggested that the two of them could reap a sizable profit by selling nearby mines back to their owners. Monihon was incensed by the offer and rebuffed Willing who quickly left town. Almost 30 years later, Monihon testified as a principal witness for the government about this in court after the fraud was exposed. Monihon relocated to Wickenburg and in March 1869, opened the Wickenburg Feed and Sale Stable.