The turn of the century, however, saw a reorganization of University departments, resulting in the creation of a single Department of Geology (1904). The succeeding five years were to be a period of considerable growth for the department. New groups of undergraduate and graduate courses were adopted, including Stratigraphy, Petrology, Chemical Geology and Vertebrate Paleontology, among others. Also in the century's first decade, the University established its Graduate School as a separate organization; no systematic program of study had formerly existed on the graduate or post-graduate level, and the three doctorates in science that had been conferred to this point were on the basis of research merit. The end of this eventful decade saw the relocation of the Geology Department from its former quarters in Nassau Hall to the newly-constructed Guyot Hall (1909). Still home to the present Geosciences Department, Guyot Hall was designed by departmental members and funded by the mother of Cleveland H. Dodge (1879), a University trustee. The stone carvings adorning the exterior of the building are thought to have been the work of the studio of Gutzon Borglum, the sculptor who created the presidential effigies of Mt. Rushmore.

The department (and the University in general) experienced a second period of growth during the 1920's, leading to the acquisition of more faculty and expanded course offerings, as well as new opportunities in fieldwork. In 1926, Richard M. Field organized Princeton's Summer School of Geology and Natural Resources, a yearly field course designed to train students in techniques of geological and geophysical research. The summer program, still extant, is currently listed in the departmental course offerings as GEO 311. In the following year, the University received funds to endow the Knox Taylor Professorship of Geography, awarded first to Professor Paul MacClintock, formerly of the University of Chicago. Another key figure in the development of the department at this time was Alexander H. Phillips, whose work on the role of trace metals in the life processes of marine organisms and the extraction of radium from Colorado carnotite were significant advances in his field.

One of the many gargoyles that grace the outside of Guyot Hall.