Cactus League (1948)

“There could be a mild upset, of course, with the October last-place championship an all-Chicago affair. That’s how many of the Grapefruit and Cactus League observers described the two Chicago entries in the big league championship competition.” J. Roy Stockton, St. Louis Post-Dispatch, April 18, 1948, p1B

NOTE: The term “Cactus league” was used informally to refer to amateur or semi-pro games played in the southwest as early as 1902. It was also used widely to describe the Mexican League beginning in 1946 when American players jumped to the league south of the border. (Ken Liss)

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1952. “Bobby Thomson…exploded his second home run of the Cactus League circuit” (The New York Times, March 26, 1952, p. 37). 

After teams began to train in 1947, Arizona-based teams were still referred to as part of the Grapefruit League. This changed in 1954 when Arizona had four teams training in the state for the first time. The terms “Cactus League” and “Cactus Loop” had begun appearing in newspaper articles two years earlier.