Dr. Mosby was born in Oregon and grew up in a small town in California. He spent much of his youth working on the family ranches in Eastern Oregon and Colusa County, California. In 1980, he married Malia, and together they attended the University of Southern California School of Dentistry. Malia graduated from the Dental Hygiene Program in 1982. Dr. Mosby received his Doctor of Dental Surgery degree in 1983. 

Over the next 29 years, he and Malia raised two sons while farming walnuts, working at times on the family ranches, and continuing to meet the dental needs of their community in rural California. Dr. Mosby is looking forward to bringing his skill and years of experience to now serve the dental needs of Lewistown and Central Montana.