Question: When did the conference the members of the Fresno State–San Diego State rivalry are both part of begin operations?
Context: The 2013 Mountain West Conference Baseball Tournament took place from May 22–26.  All six of the league's teams met in the double-elimination tournament held at California State University, Fresno's Pete Beiden Field.  It was Fresno State's first year in the league after joining from the Western Athletic Conference.  San Diego State won the tournament for the second time, earning the Mountain West Conference's automatic bid to the 2013 NCAA Division I Baseball Tournament. The 1992 Freedom Bowl was a postseason college football bowl game between the USC Trojans of the Pacific-10 Conference and the Fresno State Bulldogs of the Western Athletic Conference.  It is widely considered the biggest win in Fresno State football history.  Fresno state, led by future Super Bowl champion Trent Dilfer fell to an early deficit with a USC touchdown.  The Bulldogs quickly responded with a Lorenzo Neal touchdown and a Derek Mahoney field goal in the second quarter.  in the second half, two more bulldog touchdowns sealed a victory for Fresno State.  The Bulldogs had 241 rushing yards, 164 passing yards, 24 first downs, and over 15 minutes of possession time more than USC.  The Trojans had 88 rushing yards, 95 passing yards, and only 14 first downs. The 2009 Western Athletic Conference (WAC) football season was an NCAA football season played from September 3, 2009, to January 4, 2010.  The Western Athletic Conference consists of 9 members: Boise State, Fresno State, Hawai'i, Idaho, Louisiana Tech, Nevada, New Mexico State, San Jose State, and Utah State.  Boise State won the 2009 WAC title going 13–0, 8–0 in conference and were invited to play in the Fiesta Bowl, in which they defeated previously unbeaten TCU.  Nevada, Fresno State, and Idaho also played in bowl games, the Hawaiʻ i Bowl, New Mexico Bowl, and Humanitarian Bowl, respectively.  Nevada lost to SMU and Fresno State lost to Wyoming, while Idaho beat Bowling Green. The San Diego State Aztecs men's soccer team is a varsity intercollegiate athletic team of San Diego State University in San Diego, California, United States.  The team is an associate member of the Pac-12 Conference, which is part of the National Collegiate Athletic Association's Division I.  San Diego State's first men's soccer team was fielded in 1968.  The team plays its home games at SDSU Sports Deck in San Diego.  The Aztecs are coached by Lev Kirshner. The Fresno State–San Jose State football rivalry is a college football rivalry between the Fresno State Bulldogs football team of California State University, Fresno and the San José State Spartans football team of San José State University.  The two teams currently play annual, regularly scheduled contests due to participation in the Mountain West Conference in the west division.  In the past, Fresno State and San José State have played in conference play in the CCC, FWC, CCAA, Big West, and WAC since 1921.  Fresno State and San José State have not played in any competitions outside of conference play and non-conference scheduled meetings. The 2014 San Diego State Aztecs football team represented San Diego State University in the 2014 NCAA Division I FBS football season.  The Aztecs were led by fourth-year head coach Rocky Long and played their home games at Qualcomm Stadium.  They were members of the West Division of the Mountain West Conference.  San Diego State finished the season 7–6, 5–3 in Mountain West play to finish in a share for first place in the West Division.  However, due to Mountain West tiebreaker rules, because of their head to head loss to Fresno State they were not considered division co–champions.  They were invited to the Poinsettia Bowl where they lost to Navy 16–17. The Fresno State–San Diego State football rivalry is an American college football rivalry between the Fresno State Bulldogs football team of California State University, Fresno and San Diego State Aztecs football team of San Diego State University.  Both schools are members of the Mountain West Conference.  The winner of the game receives the "Old Oil Can" trophy. The 2014 Fresno State Bulldogs football team represented California State University, Fresno in the 2014 NCAA Division I FBS football season.  The Bulldogs were led by third-year head coach Tim DeRuyter and played their home games at Bulldog Stadium.  They were members of the Mountain West Conference and completed in the West Division.  They finished the season 6–8 overall and 5–3 in conference to tie for first place in the West Division, but due to their head-to-head win over San Diego State, they were crowned West Division champions.  They lost to Mountain Division champion Boise State in the Mountain West Championship Game.  They were invited to the Hawaii Bowl where they lost to Rice. The Fresno State–Hawaii football rivalry is an American college football rivalry between the Fresno State Bulldogs and the Hawaii Rainbow Warriors.  It is the second-oldest and most fierce rivalry in the West Division of the Mountain West Conference.  The two teams have met 49 times, with Fresno State currently leading 26–22–1.  The rivalry was surely recognized in 2016. The Mountain West Conference (MW) is one of the collegiate athletic conferences affiliated with the National Collegiate Athletic Association (NCAA) Division I Football Bowl Subdivision (FBS) (formerly I-A).  The MW officially began operations in July 1999.  Geographically, the MW covers a broad expanse of the Western United States, with member schools located in California, Colorado, Hawaii, Idaho, Nevada, New Mexico, Utah, and Wyoming.  Craig Thompson has served as Commissioner of the MW since its founding in 1999.
Answer: July 1999