Complex sentence: The stadium also boasts an all weather track that circles the playing field and is used by the Poudre School District for its many track and field events that involve not only the cities high schools but also many junior high schools and elementary schools.
Split into simpler sentences: The stadium also boasts an all weather track that circles the playing field. This is used by the Poudre School District for its many track and field events, which involve not only the city's high schools, but also many junior high schools and elementary schools.