further, the dried-up Harkra become an intermittent river, and the urban Harappan civilisation declined, becoming localized in smaller agricultural communities. Geography The northeastern part of the Thar Desert lies between the Aravalli Hills. The desert stretches to Punjab and Haryana in the north, to the Great Rann of Kutch along the coast, and to the alluvial plains of the Indus River in the west and northwest. Much of the desert area is covered by huge, shifting sand dunes that receive sediments from the alluvial plains and the coast. The sand is highly mobile due to the strong winds that rise each year before the onset of the monsoon. The Luni River is the only river in the desert. Rainfall is per year, almost all of it between June and September. Saltwater lakes within the Thar Desert include the Sambhar, Kuchaman, Didwana, Pachpadra, and Phalodi in Rajasthan and Kharaghoda in Gujarat. These lakes receive and collect rainwater during monsoon and evaporate during the dry season. The salt comes from the weathering of rocks in the region. Lithic tools belonging to the prehistoric Aterian culture of the Maghreb have been discovered in Middle Paleolithic deposits in the Thar Desert. Climate The climate is arid and subtropical. Average temperature varies with season, and extremes can range from near-freezing in the winter to more than 50º C in the summer months. Average annual rainfall ranges from 100 to 500 mm, and occurs during the short July-to-September southwest monsoon. The desert has both a very dry part (the Marusthali region in the west) and a semidesert part (in the east) that has fewer sand dunes and slightly more precipitation. Desertification control The soil of the Thar Desert remains dry for much of the year, so it is prone to wind erosion. High-velocity winds blow soil from the desert, depositing some of it on neighboring fertile lands, and causing sand dunes within the desert to shift. To counteract this problem, sand dunes are stabilised by first erecting microwindbreak barriers with scrub material and then by afforestation of the treated dunes—planting the seedlings of shrubs (such as phog, senna, and castor oil plant) and trees (such as gum acacia, Prosopis juliflora, and lebbek tree). The 649-km-long Indira Gandhi Canal brings fresh water to the Thar Desert. It was built to halt any spreading of the desert into fertile areas. Protected areas There are several protected areas in