Article: Among the first to study Russian dialects was Lomonosov in the 18th century. In the 19th, Vladimir Dal compiled the first dictionary that included dialectal vocabulary. Detailed mapping of Russian dialects began at the turn of the 20th century. In modern times, the monumental Dialectological Atlas of the Russian Language (Диалектологический атлас русского языка [dʲɪɐˌlʲɛktəlɐˈɡʲitɕɪskʲɪj ˈatləs ˈruskəvə jɪzɨˈka]), was published in three folio volumes 1986–1989, after four decades of preparatory work.

Question: When were detailed maps of Russian dialects created?
turn of the 20th century