Currently, Dr. Sellars is preparing a personal retrospective on the national parks and national park system based on his experiences and observations over a 35-year career with the Park Service. On hold until that project is completed is a companion study to Preserving Nature – a history of evolving policies and practices in the management of historic and archeological sites in the National Park System. Portions of this study have been published as Pilgrim Places: Civil War Battlefields, Historic Preservation, and America’s First National Military Parks, 1863-1900, (Eastern National Press, 2005); and “A Very Large Array: Early Federal Historic Preservation–The Antiquities Act, Mesa Verde, and the National Park Service Act,” Natural Resources Journal (University of New Mexico School of Law, Volume 47, no.2, 2007).
Sellars began his career with the National Park Service in the mid-1960s as a seasonal naturalist in Grand Teton National Park. In October 1973 he accepted a position in the Southwest Regional Office in Santa Fe, New Mexico. He spent the remainder of his Park Service career in Santa Fe, although his research, writing, teaching and other work have, in one way or another, involved virtually the entire National Park System. From 1979 to 1988, Sellars oversaw programs in history, archeology, and historic architecture for the Southwest Region, as well as Servicewide programs in underwater archeology. Special assignments have included acting superintendencies at national park units, and a liaison consultancy with the Dallas County Historical Foundation on preservation and interpretation of the Texas School Book Depository and Dealey Plaza, in Dallas, Texas, site of the assassination of President John F. Kennedy. He has visited approximately 370 of the more than 390 units of the National Park System, and is a recipient of the Department of the Interior's Meritorious Service Award and the Coalition of National Park Service Retirees' "George B. Hartzog, Jr., Award."
Sellars' articles on American history and on cultural and natural resource preservation have appeared in numerous publications, among them The Washington Post, Wilderness, National Parks, Journal of Forestry, and Landscape. He has lectured on preservation philosophy, policy and practice at many universities and conferences, and for more than a decade conducted two-week courses in historic preservation for National Park Service managers. He has given presentations at a number of special meetings, including the Thomas Moran Symposium at the National Gallery of Art, Washington, D.C.; Abraham Lincoln 197th Birthday Commemoration, Springfield, Illinois; the Greater Yellowstone Coalition Conference, West Yellowstone, Montana; and the Mesa Verde Centennial Archeological Conference (keynote address).
In 1999 and 2000, Sellars served as president of The George Wright Society – an internationally focused organization dedicated to the preservation of natural and cultural parks and preserves. For two years he was a member of the National Park Service's National Wilderness Steering Committee. He also spent two terms on the board of the Forest History Society, and served on the Historic Design Review Board for the City of Santa Fe. In 1972 he received his doctorate in American history and literature from the University of Missouri-Columbia.