Siemon William Muller (May 9, 1900 – September 9, 1970) was an American paleontologist and geologist, known for his studies on Triassic paleontology and stratigraphy, and for his work on permafrost.

Muller earned his master's degree from Stanford University in 1929, and his doctorate in 1930, studying Mesozoic ammonite fauna in the Pilot Mountains of Nevada under the direction of James Perrin Smith.

[1][2] In 1928, Muller made an initial identification of the ichthyosaur fossils found near Berlin, Nevada, although full excavations were not done until much later.

[3] Before and after World War II, Muller worked extensively with Henry G. Ferguson doing geological mapping in west-central Nevada (along with Ralph Roberts and Stanley H. Cathcart); this resulted in the publication of seven USGS geology quadrangle maps between 1951 and 1954.

[1] During World War II, Muller worked for the USGS Military Geology Unit,[4] where he studied frozen terrains such as Alaska; his Russian language skills enabled him to read the extensive Russian scientific literature on the subject.