 They are designated in high volume traffic areas where radar services are available, but not otherwise designated as class B or C airspace, such as the Palm Springs Valley in Southern California where high mountainous terrain channels air traffic into the same busy space.TRSA's can sometimes be found around class D airports as well, such as East Texas Regional Airport in Longview, TX, Chicago Rockford International Airport in Rockford, IL, and Kalamazoo/Battle Creek International Airport in Kalamazoo, MI.When VFR, pilots need not contact TRACON prior to entry or while in any TRSA, however it is recommended they do so.