Lowell Observatory is located in Arizona, home to some of the clearest, darkest skies in the USA. Lowell Observatory currently has three sites.
The original site for Lowell Observatory is on Mars Hill, in Flagstaff, Arizona (the world's first International Dark-Sky City). The Observatory was established in 1894. It is the home of the 24" Alvan Clark Refractor. This is the telescope which Percival Lowell used to sketch the surface of Mars. It was also used by V.M. Slipher for valuable research that helped establish that the Universe is expanding. This telescope is used for public outreach today: visitors peer through it to see the wonders of the heavens. Lowell Observatory is also where Clyde Tombaugh used a 13" telescope to discover Pluto in 1930. This telescope is still located on Mars Hill.
Lowell Observatory includes a research site at Anderson Mesa, 12 miles from Flagstaff. The telescopes at Anderson Mesa include the 72" Perkins Telescope, the 42" John S. Hall Telescope, the Navy Precision Optical Interferometer (NPOI) in partnership with the Naval Observatory and Naval Research Laboratory, and several others. The research at Lowell spans much of modern astrophysics, from studying tiny icy objects in our own solar system to the structure of distant galaxies.
The new star at Lowell Observatory is at a third location: Happy Jack, a dark site in the Coconino National Forest, 40 miles from Flagstaff. The Discovery Channel Telescope (DCT), a partnership between Discovery Communications and Lowell, is 4.3 m in diameter. It began observing the heavens in April, 2012. The DCT is equipped to take spectroscopic and imaging observations at the same time. It is now the flagship telescope for research at Lowell.
Adapted from the Lowell Observatory website, lowell.edu.