The area is predominantly mountainous and composed of various limestones interspersed with massive intrusions of granite and smaller outcrops of quartzite and schist. Elevations range from about at the Vajiralongkorn Reservoir in the south of the sanctuary to its highest peak, Khao Tai Pa, at . Major rivers are the Mae Klong and the Mae Chan which originate in the Umphang Wildlife Sanctuary and join in Thung Yai into the Upper Khwae Yai which feeds the Si Nakharin Reservoir. Various smaller rivers in the south and southwest feed the Vajiralongkorn Reservoir while in the northwestern part of the sanctuary the Mae Kasat and the Mae Suriya flow into Burma.