Statement of Significance (as of designation - December 21, 1965):
Founded in 1894 by Percival Lowell, this relatively small observatory was at the time the one significant center of pure scientific research in the Southwest. Here, Lowell studied Mars (and theorized that it was inhabited by intelligent beings) and performed the computations that led to the discovery of Pluto; Dr. A.E. Douglass' research led to the modern science of dendrochronology; and, in 1912, V.M Slipher discovered that the universe was expanding. The observatory is still in operation.