Abstract(#br)Karst landforms cover a considerable area of the Earth's surface. With increasing population and demand for further land exploitation, the prospect of being affected by karsts has increased dramatically over the past decades. Among karst landforms, salt karsts show higher vulnerability and faster evolution in the human life-span. In Iran, most of salt karst studies have been carried out in the south (mainly Zagros). Contrariwise, the northern and central parts of the country have been rarely studied. This study investigates a salt karst system in the northeastern part of the Central Iran. Field investigation and satellite image analysis of the area revealed a salt karst in the Upper Red Formation (URF) comprising elements of a mature karstic system including dolines, ponors,... caves, shafts, valleys, poljes, springs, and streams. Tectonics by creating open fractures in impermeable salts provided conduits for fluid transport and development of the karst. Since salts are highly soluble and disappear very soon, arid climate in the studied area led to the preservation of the salt karst. Although the area is a cold desert with small amounts of precipitation, it is hydrologically active. This is ascribed to the increased water efficiency by the karst system that immediately funnels the runoffs into the ground and prevents from evaporation. Water efficiency is amplified by an impermeable substrate of the karst and timing of the precipitation. The studied karst partly underlies the Tehran–Mashhad railway which endangers the infrastructure, and can cause failure and casualties. Since the salt bearing URF extends throughout large parts of Central Iran, this study suggests comprehensive geomorphological, hydrogeological, and geophysical studies of this formation for providing hazard maps.