South-central Alborz is a language transition zone bounded by Persian, Māzandarāni, Central Caspian and Tatic language groups. In the lofty valleys of this area, separated from Tehran by a mountain chain, rest villages with vanishing dialects that show various degrees of affinity with the neighbouring languages. The two dialects studied here, namely Velātruyi and Gachsari, belong to two different language groups, despite their geographical proximity on the upper Karaj valley. This study is founded on the texts collected by the late Ann Lambton in 1936, and conducts an areal, historical, and synchronic study of these dialects and attempts to provide an accurate translation of the texts, which are reproduced here together with glossaries.