He and Kenneth McKenzie’s other children were sent to the Red River settlement in Canada for schooling. Afterward, Owen returned to the upper Missouri River and, in 1843, was working as a hunter for the American Fur Company at Fort Union, North Dakota. He was said to have been a skilled horseman and a first-rate shot.
He was then placed in charge of a fur trade post on the White River. In the winter of 1862-63, he was in charge of a small post for the La Barge, Harkness and Company on the Missouri River above Fort Union. In the summer of 1863, he was sent to take charge of Fort Galpin at the mouth of the Milk River in present-day South Dakota. There, he got into a dispute with Malcolm Clarke and his son, Horace, over money matters. Malcolm Clarke was a rancher and fur trader who worked in association with the American Fur Company. Own and Malcolm had a history of frequent arguments. In 1863, the argument turned into a brawl, and Malcolm Clark then shot and killed McKenzie.
After the murder, Clarke fled the area to escape the revenge of McKenzie’s many friends. Clarke then moved his family to the Rocky Mountains and undertook ranching with his second wife, a mixed-race Blackfoot woman named Good Singing. They established the Clarke Horse and Cattle Ranch in 1864.
On August 17, 1869, Malcolm Clark was killed by Piegan Indians. This created a climate of unrest in the region, as outraged white settlers demanded that the government protect them and suppress the outlaw Blackfeet. This led to the Marias Massacre in Montana on January 23, 1870.