The economic depression of the 1930's brought about a temporary reduction of department personnel, but did not prevent the organization of an unprecedented array of Princeton-led field projects in geosciences. Among these were a series of expeditions to Newfoundland beginning in 1932 under the direction of faculty member A.K. Snelgrove. The field work was jointly conducted by faculty, graduate and undergraduate students, encompassing several projects in different parts of the island. Snelgrove was subsequently appointed by the Newfoundland Government to direct the Newfoundland Geological Survey, a post which he held simultaneously with his professorship at Princeton. This led to a cooperative and long-lasting relationship between the Survey and Princeton's Department of Geology.

Another major undertaking in field research at this time was the "Red Lodge Project" (1930), initiated by Richard M. Field and fellow faculty member W. Taylor Thom. Red Lodge and its successor, the Yellowstone-Bighorn Research Association (1936), were designed to further geological knowledge both in general and about that region in particular. In the tradition of Field's "Summer School" program, one of the project goals was to provide a favorable field situation for the training of students. Red Lodge and YBRA proved to be highly successful; by 1941 over 44 colleges and universities had been represented in these projects by faculty, graduate and undergraduate students. Although he would remain active with Red Lodge, Field went on to conduct measurements of gravitational anomalies in the Caribbean, marking a significant chapter in Princeton's long-standing involvement in the study of that region's geology.

In 1932, Field recruited Harry Hammond Hess, then only a few months away from his Ph.D., to assist in the research. After Hess took his doctorate, he joined the department faculty, succeeding Alexander Phillips in 1934 as Professor of Mineralogy and later serving as department chair from 1950-66. Hess remained actively interested in ocean basin research throughout his entire career; after the Second World War, his continued work in this field would eventually lead to his ground-breaking theory of sea floor spreading, which contributed significantly to the understanding of plate tectonics and continental movement.

In 1942, the entry of the United States into the Second World War prompted the University to adopt an accelerated study program, allowing its students to complete their coursework within three years or less. In spite of this, the Department of Geology saw a marked decrease in enrollment as more and more students interrupted their studies to enter the armed services or undertake work otherwise related to the war effort. An even sharper decrease in department faculty necessitated special courses during the Winter Reading Period, doubled enrollment for several classes and field expeditions, and a larger program of study for the summer term. The department also responded to the national crisis by adopting courses specifically designed for military purposes, particularly army topography and the interpretation of aerial reconnaissance photography. These were offered to a group of students largely composed of enlisted men. The war had many long-lasting effects on the department, not the least of which was an increased awareness of the importance of instruction in the relationships between geosciences and culture, global economics and public policy.