Complex sentence: They are founding members of the Great West League and began play in 2013 at Harry & David Field replacing the now-defunct Southern Oregon Riverdawgs and as an expansion team in the West Coast League, where they played from 2013 to 2015.
Split into simpler sentences: They are founding members of the Great West League and began play in 2013 at Harry & David Field. They begin play as an expansion team in the West Coast League, where they played from 2013 to 2015.