Leon was the son of George Atwood, born in the Yucaipa valley November 19, 1886.  He attended schools in San Bernardino as a boy, but plans to attend the University of Michigan were scraped in favor of marriage.  He married Frances Alma, daughter of W. S. Hooper, in San Bernardino on November 11, 1908.  His father's involvement in Yucaipa provided a prime opportunity to persue farming and grow apples, and he did so at a very early date, being the first to ship apples out of the valley.  With his father he owned several thousand acres of Yucaipa Valley, and also held property in San Bernardino and Rialto.

During the first world war he was appointed chief of the American Protective League for San Bernardino County, which was involved in secret service work for the government.  Later he was appointed special agent for the Department of Justice in charge of Riverside, Inyo and San Bernardino counties.  He remained civically active throughout his life, as president of the Better City Club of San Bernardino, member of the Native Sons of the Golden West, the Elks, YMCA, and charter member of the Newport Harbor Yacht Club.

His death occurred while returning home from Los Angeles by electric train when it crashed into a truck hauling rocks.

Leon and Frances had three children: Leon Arnold, Jr., Frances Mary and Stanford William.