Duncan McDuffie (September 24, 1877 – 1951) was a real estate developer, conservationist, and mountaineer based in Berkeley, California, United States.
McDuffie is best known for developing the Claremont and Northbrae neighborhoods of Berkeley and St. Francis Wood district in San Francisco. His upscale developments were laid out as "residential parks," with streets that follow the contours of the hills and power lines that run underground.
McDuffie was also a notable conservationist. He was president of the Sierra Club from 1928 to 1931 and from 1943 to 1946.
In 1934 McDuffie helped create the East Bay Regional Park District in the Berkeley Hills.
Duncan McDuffie helped establish the California state park system with the help of his friend, Governor C. C. Young. He won the Pugsley Medal for his service on the California State Parks Commission.
McDuffie was an accomplished mountaineer in the Sierra Nevada. He made first ascents of Mount Abbot and Black Kaweah.
Along with Joseph N. LeConte and James S. Hutchinson, he pioneered a high mountain route in 1908 from Yosemite National Park to Kings Canyon, roughly along the route of the modern John Muir Trail. In 28 days, they completed a trip of 228 miles through the high mountains, including several previously unexplored sections.