Eastwood was born in Toronto, Canada, but moved to California with her family in 1870. She showed an early interest in natural history, and in 1892 she began working as a volunteer at the California Academy of Sciences. In 1894, she was hired as the Academy's curator of botany, a position she held until her retirement in 1945.
During her time at the Academy, Eastwood made significant contributions to the field of botany. She conducted extensive field research, collecting thousands of plant specimens from throughout California and the western United States. She also published numerous scientific articles and books, including "A Handbook of the Trees of California" (1905), "The Flora of the Santa Cruz Peninsula" (1909), and "The California Flora" (1914).
In addition to her scientific work, Eastwood was also an active member of the conservation movement. She was a founding member of the California Botanical Society and the Save the Redwoods League, and she served as president of the Sierra Club from 1923 to 1925. She was also a vocal advocate for the protection of California's native plants, and she played a key role in establishing several state parks and nature preserves.
Eastwood was a highly respected and influential figure in the field of botany. She was awarded numerous honors and awards, including the Linnaean Society of London's Gold Medal in 1922 and the American Association for the Advancement of Science's Margaret Mead Award in 1947. She died in San Francisco in 1953 at the age of 94.
Eastwood's legacy continues to inspire and influence botanists and conservationists today. She was a pioneer in the field of botany, and her work has made a lasting contribution to our understanding of the flora of California and the western United States. She was also a tireless advocate for the protection of nature, and her work helped to lay the foundation for the conservation movement in California.