In 1915, the Mackmen played as members of the short–lived Class D level Rio Grande Association, with El Paso finishing in second place, as the league permanently folded during the season.
The league franchises and structure were established after an organizational meeting was held at the Hotel Sheldon, in El Paso, Texas.
[2] The Rio Grande Association was formed with six franchises, based in Texas, Arizona and New Mexico: the Albuquerque Dukes, Douglas Miners, Las Cruces Farmers, Phoenix Senators and Tucson Old Pueblos joined El Paso as the charter members.
[8] At a league meeting held in El Paso, on July 5, 1915, the Rio Grande Association was folded due to continuing financial losses.
[9] The El Paso Mackmen ended their Rio Grande Association season with a record of 36–22, placing second in the final standings.
[15] In a game at Rio Grande Park on June 20, 1915, Byrd Lynn, a catcher for the Phoenix Senators threw his bat at the umpire.