The West was the last area in the United States to be reached during the gradual westward expansion of English-speaking settlement and its history shows considerable mixing of the linguistic patterns of other regions. As the settlement populations are relatively young when compared with other regions, the American West is a dialect region in formation.
The Western dialect of American English is somewhat variable and not necessarily distinct from "General American." Western American English is characterized primarily by two phonological features: the cot–caught merger (as distinct from most Northern and Southern U.S. English) and the fronting of // but not // (as distinct from most Southern and Mid-Atlantic American English, in which both of those vowels are fronted, as well as from most Northern U.S. English, in which both of these remain backed).
Like most Canadian dialects and younger General American, /ɑ/ allophones remain back and may be either rounded or unrounded due to a merger between // and // (commonly represented in conservative General American, respectively, so that words like cot and caught, or pod and pawed, are perfect homophones (except in San Francisco). Unlike in Canada, however, the occurrence of Canadian raising of the // and // diphthongs is not as consistent and pronounced. A significant minority of Western speakers have the pin–pen merger or a closeness to the merger, especially around Bakersfield, California, though it is a sound typically associated with Southern U.S. dialect, which influenced the area. The West is entirely rhotic and the Mary–marry–merry merger is complete (as in most of North America), so that words like Mary, marry, and merry are all pronounced identically because of the merger of all three of those vowels' sounds when before r (towards ).
Several sub-types of the Western dialect exist or appear to be currently in formation. A noticeable California Vowel Shift has been observed in the English of some California speakers scattered throughout the state, though especially younger and coastal speakers. This shift involves two elements, including that the vowel in words like toe, rose, and go (though remaining back vowels elsewhere in the Western dialect), and the vowel in words like spoon, move, and rude are both pronounced farther forward in the mouth than most other English dialects; at the same time, a lowering chain movement of the front vowels is occurring (identical to the Canadian Vowel Shift), so that, to listeners of other English dialects, sit may approach the sound of set, set may approach sat, and sat may approach sot. This front-vowel lowering is also reported around Portland, Oregon, the hub of a unique Northwestern variety of American English that demonstrates other similarities with Canadian English. A trend evident particularly in some speakers from the Salt Lake City, Utah and Flagstaff, Arizona areas, as well as in some Californian and New Mexican English, is the completion or transition towards a full–fool merger.
Studies demonstrate that gender, age, and ability to speak Hawaiian Creole (a language locally called "Pidgin" and spoken by about two-fifths of Hawaii residents) correlate with the recent emergence of different Hawaiian English accents. In a 2013 study of twenty Oʻahu-raised native English speakers, those who do not speak Pidgin or are male were shown to lower // and //; younger speakers of the first group also lowered //, and younger participants in general backed //. Though this movement of these vowels is superficially similar to the California Vowel Shift, it is not believed to be due to a chain shift, though Hawaii residents do have a cot–caught merger, at least among younger speakers. Unlike most Americans, Hawaii residents may not demonstrate any form of /æ/ tensing (even before nasal consonants, as with most Western Americans).