Puget Sound only Puget Sound proper but also for waters to the north, such as Bellingham Bay and the San Juan Islands region. The term "Puget Sound" is used not just for the body of water but also the Puget Sound region centered on the sound. Major cities on the sound include Seattle, Tacoma, Olympia, and Everett, Washington. Puget Sound is also the third largest estuary in the United States, after Chesapeake Bay in Maryland and Virginia, and San Francisco Bay in northern California. In 1792 George Vancouver gave the name "Puget's Sound" to the waters south of the Tacoma Narrows, in
Puget Sound faults geologic province is the approximately 50 million year (Ma) old marine basalts of the Crescent Formation, part of the Siletzia terrane that underlies western Washington and Oregon. East of Puget Sound the basement of the Cascades province is various pre-Tertiary (older than 65 Ma) metamorphic rock. Somewhere between Puget Sound and Cascades foothills these two geological provinces come into contact. As the juxtaposition of various disparate tectonic structures in northwest Washington requires significant strike-slip movement, it is further expected that this contact will be a major fault. The northern end of the Crescent Formation (aka Metchosin Formation) has been identified