Familiar with the direct historical approach, Jelks minored in history while completing his Ph.D., interested largely in the location of Spanish colonial sites in Texas.
Excavations at the Stansbury Site[3] in Hill County, Texas led Jelks to conduct library research to identify trade goods that were found.
[2] After completing his Ph.D., Jelks was offered a position teaching the archaeology of Texas in the newly created anthropology department at Southern Methodist University.
Jelks was hired as an associate professor, a position he held from September 1965 to 1968, and he taught both Texas prehistory and a graduate seminar in historical archaeology.
[2] While teaching at Southern Methodist University, Jelks spent his summers working as an archaeologist for Parks Canada, excavating British artifacts of the early to mid-19th century at Signal Hill, Newfoundland.
The conference drew a total of 112 attendees, with presentation of seventeen papers by scholars including Charles Cleland, James Deetz, Bernard Fontana, J.C. Harrington, and Roderick Sprague.
In 1983, Jelks and ISU history professor Carl Ekberg did identify the first site of the French Fort de Chatres, built along the Mississippi River in southern Illinois in 1719.
West Point hoped to use archaeological data as a basis for restoring Revolutionary War period fortifications in honor of the approaching United States Bicentennial celebration.
This frightened a number of archaeologists and led to the Airlie House Conference of 1974, sponsored by the Society for American Archaeology and financed by the National Park Service.
Jelks, elected as SOPA's first president, then presented at the SAA annual meeting in spring 1976, urging members to join the new registry.
[2] Jelks' other fieldwork of note included excavations at the Grand Village of the Kickapoo (late 18th-early 19th century) in McLean County, Illinois, the De Brum copra plantation[5] (early 20th century) at Likiep Atoll in Micronesia, and America's first dude ranch, the Bar-B-C Dude Ranch[6] (established in 1912), in Grand Teton National Park, Wyoming.