The Mountain States region has had a rich and entertaining history of professional baseball since the turn-of-the-century. Pro ball began in 1901 with one season of the Utah League (Ogden was the champion) and then the Intermountain League’s one season in 1909, (Helena won the pennant). A more stable league began when the Union Association began play beginning in 1911 and managed to stay in operation through 1914. In that span, Great Falls won two pennants, while Missoula, Salt Lake City, and Ogden won or tied for one pennant apiece.
Formed in 1926, the Utah-Idaho League lasted for three seasons, with Idaho Falls winning league championships in 1926 and 1927, with Salt Lake City winning in 1928.
The current Pioneer League was formed in 1939 with six teams: Boise, Lewiston, Ogden, Pocatello, Salt Lake City, and Twin Falls, who won the league’s initial championship. Since that time the Pioneer League generally maintained its base states of Montana, Idaho, Colorado and Utah, although from time-to-time teams from Canada and Wyoming have entered the league.
In 1964 the Pioneer League, with only four teams, was downgraded to Rookie League status league until 1968 when the Salt Lake City Giants joined to form a rather unwieldy five-team league. After expanding to seven teams in 1969 with the addition of teams in Billings (the Mustangs) and Great Falls, the Pioneer League dropped to six teams in 1970, and back to four teams in 1971
The 1990s saw relative stability return to the Pioneer League, although team affiliations changed regularly. Over the years, the Dodgers, Reds, Brewers, Diamondbacks, Braves, Yankees, Cardinals, White Sox, Angels, A’s, Phillies, Padres, Expos, Giants and Blue Jays have affiliated with PBL clubs.
After the 2018 season, the PBL maintained eight teams. The Helena Brewers relocated to Colorado Springs, Colorado where they now play as the Rocky Mountain Vibes.
The 2020 season was postponed due to the COVID-19 pandemic, making the 2019 season the league's last as an MLB-affiliated league. The PBL, however, was converted to an independent league with MLB Partner League status. The league will continue with the eight franchises using the same identities, with the exception of the Orem Owlz relocating to Windsor, Colorado, as the Northern Colorado Owlz. Joining the Pioneer League for 2021 will be the Boise Hawks from the Northwest League.