On which mountain observatory did Edwin Hubble make most of his observations?

Edwin Hubble made most of his landmark observations at Mount Wilson Observatory in California. The observatory's high elevation and relatively dark, steady skies made it one of the world's leading astronomical facilities during the early twentieth century.

Hubble worked primarily with the 100-inch Hooker Telescope, completed at Mount Wilson in 1917. With that instrument, he identified Cepheid variables in Andromeda and other galaxies, demonstrating that they lay outside the Milky Way. He later combined galaxy distance estimates with redshift data to establish the observational basis of the expanding-universe relationship now called Hubble's law.

Mount Wilson was also associated with other major advances, including George Ellery Hale's solar observations and the work of Vesto Slipher and Milton Humason, whose measurements contributed to studies of galaxy motions. Hubble did not make most of these famous observations at Palomar Observatory: Palomar's 200-inch Hale Telescope opened later, in 1948, after Hubble's principal research period. Mauna Kea became a major observatory site much later as well.