Complex sentence: Chillits is an annual ambient music campout party, usually held every September from 1999 through 2009 at a private retreat center near Willits, California, USA and at an alternate location in Plymouth, California, USA from in 2010 to 2012.
Split into simpler sentences: Chillits is an annual ambient music weekend-long outdoor party, usually held every September, starting in 1999. From then through 2009, it was held at a private retreat center near Willits, California, USA, and at an alternate location in Plymouth, California, USA from 2010 to 2012.