The medics ruled out further field work in the jungle, and Martin had to limit his scientific career to continental United States. By this time he was already well known to Midwestern historians and archaeologists. In 1928 Martin had already begun his ten-year research in Montezuma County, Colorado but in the summer of 1929 the Department of the Interior denied him permission to excavate Lowry Pueblo. The DOI argued that Martin's employer, the State Historical Society of Colorado, was financially unable to complete the excavation. According to Nash, this setback motivated Martin to seek a stronger employer. Indeed, on August 22, 1929 Berthold Laufer of the Field Museum of Natural History offered Martin a job at the Museum's department of anthropology and Martin readily accepted the offer. Nash wrote that the Museum "almost certainly" planned to use Martin in the upcoming modernization of the museum exhibits in its new building in Grant Park. Martin "spent a remarkable amount of time" in rearranging the exhibition and public outreach campaigns that preceded and accompanied the Century of Progress exhibition of 1933–1934 and wrote the 122-page guide to the "Archaeology of North America" collection. After Laufer's suicide in 1934 Martin became the acting curator of the department and temporarily assumed Laufer's role in presenting the Oriental collections to the public. Martin chaired the department if from 1935 to 1964 and remained with the Museum until 1972. According to Nash, "no other Field Museum curator, in anthropology or any other department, was as visible on the exhibition floor, in "Field Museum News", or in the Chicago newspapers during" the pre-war period. Martin was never married and had no children. Towards the end of his life, in 1972, Martin moved to Tucson, Arizona and for a short time worked at the University of Arizona. The University then employed another, and unrelated Paul S. Martin. This other Paul S. Martin (who died in 2010 and had already established himself as an unorthodox thinker in the early 1970s) also studied prehistoric, pre-Columbian America. Paul Sidney Martin died in 1974 of heart failure and coronary artery disease. Martin's Montezuma County project, which spanned from 1928 to 1938, is "enormous by modern standards". In the first season his team of six diggers excavated thirty rooms, four kivas, eight towers and twelve waste heaps at Cutthroat Castle. He developed a theory that the Pueblo ruins actually belong to two types: an earlier known type built on open mesas and a different, rim-rock type of settlement built on the ledges of canyons.