The Rocky Mountain Junior A Hockey League was formed in 1990, to begin play for the 1990-91 season, when the Peace Cariboo Junior Hockey League doubled in size by taking in a portion of the Kootenay International Junior B Hockey League.
The RMJHL folded after the 1998-99 season and its remaining teams split, some merged into the British Columbia Junior Hockey League and the others into the Kootenay International Junior B Hockey League.
The RMJHL Champions have never advanced past the Mowat Cup. In fact the one and only game the RMJHL won, versus the BCHL, came in 1999, when the Kimberley Dynamiters defeated the Vernon Vipers.
In 1975, the Quesnel Millionaires and Prince George Spruce Kings joined the Peace Junior B Hockey League. The PJBHL already included the Fort St. John Huskies, Dawson Creek Canucks, and Grande Prairie North Stars. Previously, Fort St. John won the Cyclone Taylor Cup as British Columbia Jr. B Champions in 1969 as a member of the Peace Jr. B League. With the expansion, the PJBHL became the Peace-Cariboo Junior Hockey League. The first championship of the new PCJHL was won by Prince George, but Quesnel won the league and the Cyclone Taylor Cup as BC Champions in 1977, 1978, and 1979.
In 1980 the PCJHL became a Junior "A" League, one season after the British Columbia Junior Hockey League and Pacific Coast Junior Hockey League merger. The league's most successful team, by far, was the Prince George Spruce Kings. Every season, their playoff champion earned the right to play for the Mowat Cup, the British Columbia Junior "A" Title. The Peace Cariboo JHL / Rocky Mountain JHL was eligible for both the Centennial and Royal Bank Cups, the Junior "A" National Title.
In 1991, the Peace Cariboo league doubled in size when it took in a portion of the Jr. B Kootenay International Junior Hockey League and renamed itself the Rocky Mountain league. The original teams to the North would form the Peace-Cariboo Division, while the newer teams to the South would form the Kootenay Division.
In 1995, the Trail Smoke Eaters walked away from the league and joined the British Columbia Hockey League. In 1996, the entire RMJHL's Peace-Cariboo Division exited the RMJHL's Kootenay Division. The Prince George Spruce Kings and Quesnel Millionaires joined the BCHL, the Grande Prairie Chiefs opted for the Alberta Junior Hockey League, the Williams Lake Mustangs went defunct, and the Fort St. John Huskies folded (to make way for a Senior team).
To fill the void when the Peace-Cariboo Division folded in 1996, the Castlegar Rebels joined the RMJHL. In 1998, however, the Rebels would return to the KIJHL(Junior B) and the Cranbrook Colts would fold to make way for the Western Hockey League's Kootenay Ice. With 4 teams left in RMJHL, Creston Valley Thunder, Kimberley Dynamiters, Nelson Leafs, and Fernie Ghostriders played an interlocking schedule with the America West Hockey League of USA Hockey.
On February 12, 1999, the commissioner of the RMJHL, Bronco Horvath, presented a letter to the management of the British Columbia Hockey League proposing the four remaining teams join the BCHL as a "Kootenay Division". The proposal was universally rejected by the BCHL.
After the 1998-99 season, Creston Valley Thunder took a one-year hiatus which forced the RMJHL to fold. (The Nelson Leafs joined to the KIJHL, Kimberley Dyanamiters and Fernie Ghostriders joined the AWHL for the 1999-00 season.
The Kimberley Dynamiters joined the KIJHL in 2001, while Fernie Ghostriders moved to the North American Hockey League in 2003 before joining the KIJHL in 2004. Creston Valley Thunder returned to hockey after one year off in 2000 with the KIJHL.