The original Eugene Emeralds and Eugene Larks were members of the Northwest League (and Far West League), and played as affiliates mostly for the San Francisco Giants and Philadelphia Phillies. They continued to play at Bethel Park from their inception in 1950 until the end of the 1968 season when it was announced that a huge change was coming to Major League Baseball.  The National League would be expanding by two new teams in 1969… the Montreal Expos and the San Diego Padres. The Padres had up until
  that point been a Triple-A Pacific Coast League team, but were now being "promoted" to the Major Leagues. While that was great news for the people of San Diego, there was one small technical caveat. What about the "Triple-A Padres team"? The whole team wasn't going to be promoted to the Majors… coaches, players and all. There had to be some sort of hand over of the old team. After all, the Pacific Coast League needed more than ever to maintain this established Triple-A franchise, as well as add two more as two new teams came into the National League.