This is because the ancestors of the Navajo originate from the Athabaskan region (located in modern-day Canada and Alaska), and as a result they were relatively late in arriving to the Southwest compared to their Puebloan neighbors.
Languages in the Tanoan and Apachean families, and additionally Hopi, can be compared to relatives not affected by this particular region's areal features as a reference for changes due to contact.
[3][7] Sherzer suggests that contact led to Acoma Keres sharing glottalized sonorants and glides with Navajo.
[1] Keresan may be the common source of glottalized nasals and semivowels in Navajo, and the development of /r/ in dialects of Tewa and Tiwa and possibly Hopi.
[1] Linguist Paul Kroskrity argues for diffused Apachean traits in Tewa, such as the passive marked by prefixes that are structured differently from those of other Tanoan languages.
[13][14][10][11] This can be seen in the following example provided by Kroskrity:[15][14][10][11] sen-bíman-POSSkʰawsongsen-bí kʰawman-POSS song'(a) man's song'bisóódipigbi-tsiPOSS-fleshbisóódi bi-tsipig POSS-flesh'the pig's flesh'This paralleling morpheme is also used in these languages' postpositional constructions.