Josiah Dwight Whitney (November 23, 1819 – August 18, 1896) was an American geologist, professor of geology at Harvard University, and chief of the California Geological Survey (1860–1874).
Whitneyw as the foremost authority of his day on the economic geology of the U.S. Mount Whitney, the highest point in the continental United States, and the Whitney Glacier, the first confirmed glacier in the United States, on Mount Shasta, were both named after Whitney.
Born in Northampton, Massachusetts, Whitney was the oldest of 12 children. His father was Josiah Dwight Whitney (1786–1869) of the New England Dwight family. His mother was Sarah Williston (1800–1833). He was the brother of grammarian and lexicographer William Dwight Whitney (1827–1894). He was educated at a series of schools in Northampton, Plainfield, Round Hill, New Haven and Andover.
He studied chemistry, mineralogy and astronomy at Yale. After graduation in 1839, he continued to study chemistry in Philadelphia, and in 1840 he joined a geologic survey of New Hampshire as an unpaid assistant to Charles T. Jackson. In 1847, he and John Wells Foster were hired by the US Government to assist Charles T. Jackson in its survey of the Lake Superior land district of northern Michigan, which was about to become a major copper and iron mining region. When Jackson was dismissed from the survey, Foster and Whitney completed it in 1850 and the final report was published under their names.