After World War II, Marshall’s father went to work for the Santa Fe Railroad. From 1947 to 1955, the Trimble family lived in the northern Arizona town of Ash Fork, on the Santa Fe mainline. Times were hard. To make ends meet his mother went to work as a waitress in a road house café. The first three years were spent living in a small, two room trailer house with a lean-to porch and an army surplus tent with no running water or plumbing.
Marshall considers those hardscrabble years in Ash Fork as "character-building." He still considers Ash Fork his hometown and returns there often to assist in community projects.
December 7, 1956, at the age of seventeen, Marshall joined the Marines and considers that experience among the most meaningful and significant of his life. He was one of three in a 75-man platoon to win a meritorious promotion upon graduating from boot camp. The Marines gave Trimble a strong sense of duty, ethics and patriotism that continues to this day. The Marines instilled in him that through hard work and persistence he could become anything he wanted to be. . Trimble says, “ At graduation Staff Sergeant Fuller walked up to me an shook my hand. “You’ll do well,” he said, “not just in the Corps but whatever else you do with your life. Never forget what you learned here.”