Question: When did the conference the UNLV Runnin' Rebels are a member of begin operations?
Sentence (from "1989–90 UNLV Runnin' Rebels basketball team"): The team played its home games in the Thomas & Mack Center, and was a member of the Big West Conference; it would join the Western Athletic Conference in 1996 and become a charter member of its current conference, the Mountain West Conference, in 1999.
Relevant evidence: Yes