Lyndon B. Johnson National Historical Park is made up of two districts (the Johnson City District in Blanco County and the LBJ Ranch District in Gillespie County), each lying in the Pedernales River Valley, which cuts through a geologic region known as the Llano Uplift. The area is characterized by hills covered with juniper and oak, with elevations ranging from 1,000-2,500 feet above sea level. The climate is dry, sub-humid: Blanco County averages 34 inches of rain per year and Gillespie County, 27.44 inches. The summers are generally hot and the winters mild. The average length of the growing season is 234 days in Blanco County and 219 days in Gillespie County. The average annual free water evaporation is 58 inches in Blanco County and 62 inches in Gillespie County.