Leffingwell first traveled to polar regions as chief scientist for the 1901 Baldwin-Ziegler Expedition. Although they failed in their quest to reach the North Pole from Franz Joseph Land, his participation prepared him for future endeavors. He experienced the dangers of living and traveling in extreme conditions, learned to operate delicate scientific instruments in freezing temperatures, and befriended fellow explorer Ejnar Mikkelsen.

Eager to investigate rumors of land north of Alaska, Mikkelsen and Leffingwell organized the 1906 Anglo American Polar Expedition. Supporters included geographic societies, Alexander Graham Bell, and John D. Rockefeller. Although the Arctic environment pushed the men to their limits, they were able to determine the edge of the continental shelf--a significant geographic discovery.

Laboring in the harsh climate of northeastern Alaska along the North Slope of the Brooks Range, the driven, risk-taking young geologist pioneered research in ground ice (often called permafrost), surveyed and documented the geography of the coastline and interior, observed birds, and collected wildlife specimens for the Smithsonian Institution and other organizations. His groundbreaking work continues to inform scientists and scholars today.

For Leffingwell's biography, author Janet R. Collins consulted his journals and professional reports, family papers and memories, and published and unpublished writings of Alice Barnard, Vilhjalmur Stefansson, and Ejnar Mikkelsen.