As part of Tucson's Birthday celebration, this event explores the role of the Empire Ranch and La Posta Quemada in shaping modern Tucson and Southern Arizona, at 2 p.m., Sunday, Aug. 7. A presentation about ranching in the late 1800s, when the Empire ranch covered most of what are now Pima, Cochise and Santa Cruz counties, is followed by a walking tour of today's Empire Ranch and La Posta Quemada. Free with $5 per car (six persons) park entrance fee. E-mail [email protected] or visit tucsonsbirthday.org for more information.