September 24th. Back by popular demand, the Susanville Symphony will once again perform on the lawn of the historic Lassen County Courthouse. Bring your picnic baskets, your folding chairs and tables for this spectacular outdoor event. A one of a kind in Lassen County. Music from Holst: The Planets, John Williams Star Wars, Bizet's Carmen and more! The weather in Lassen Count at this time of year is nearly always perfect: an autumn day with blue skies, bright sun, green grass and lawn chairs as far as the eye can see.