[1][2] He was born at Chicago, Illinois on June 4, 1880, the son of Isaac Simeon Blackwelder and Alice Gertrude née Boughton.

[5] As a youth, Eliot developed an interest in entomology, and by the age of 15 he was a member of the American Ornithological Union.

[6] Immediately following graduation, he was invited by Rollin D. Salisbury to accompany him on an expedition to the Rocky Mountains.

The trip lasted more than a year, crossing Asia, northern China, and ending on the Yangtze River.

After 1909 he worked as a geologist performing studies in northern Utah, southeastern Idaho, and western Wyoming.

[11] He became the chief geologist for the East Butte Copper Mining Company in September 1919, remaining there until 1921.

[16] During 1921–1922, he partnered with Lewis A. Parkhurst and George C. Humphrey to establish the Teton Syndicate, where Blackwelder served as a manager.

[17] In 1922, he was named full professor[9] at Stanford University, filling the chair of the geology department to replace the retiring Bailey Willis.

[1][2] During his time at Stanford, Blackwelder made geological explorations of the Sierra Nevada range and its glacial valleys.

He explored the arid regions of the southwest, writing papers on the origins and evolution of desert landscapes.