In the late 1930s he conducted major excavations in the Savannah, Georgia area at the Irene site as part of Depression-era archaeology program.
During his career Caldwell also served as a professor in the United States and for a year in Iran as a Fulbright scholar.
During this time he worked with several other prominent Georgia archaeologists, including Antonio J. Waring, Jr., Preston Holder and Catherine McCann.
In the late 1930s he also visited Stallings Island with Waring, Jr. and collected a large number of artifacts during a surface survey.
This survey located and excavated hundreds of archaeological sites that were later inundated and destroyed when man-made lakes were created.