<P> South of the northern highlands and west of the Indus River plain are the Safed Koh Range along the Afghanistan border and the Sulaiman Range and Kirthar Range, which define the western extent of the province of Sindh and reach almost to the southern coast . The lower reaches are far more arid than those in the north, and they branch into ranges that run generally to the southwest across the province Balochistan . North - south valleys in Balochistan and Sindh have restricted the migration of peoples along the Makran Coast on the Arabian Sea east toward the plains . </P> <P> Several large passes cut the ranges along the border with Afghanistan . Among them are the Khojak Pass, about eighty kilometres northwest of Quetta in Balochistan; the Khyber Pass, forty kilometres west of Peshawar and leading to Kabul; and the Broghol Pass in the far north, providing access to the Wakhan Corridor . </P> <P> Less than one - fifth of Pakistan's land area has the potential for intensive agricultural use . Nearly all of the arable land is actively cultivated, but outputs are low by world standards . Cultivation is sparse in the northern mountains, the southern deserts, and the western plateaus, but the Indus River basin in Punjab and northern Sindh has fertile soil that enables Pakistan to feed its population under usual climatic conditions . </P> <P> The name Indus comes from the Sanskrit word sindhu, meaning ocean, from which also come the words Sindh, Hindu, and India . The Indus, one of the great rivers of the world, rises in southwestern Tibet only about 160 kilometres west of the source of the Sutlej River, which first flows through Punjab, India and joins the Indus in Pakistani Punjab, and the Brahmaputra, which runs eastward before turning southwest and flowing through India and, Bangladesh . The catchment area of the Indus is estimated at almost 1 million square kilometres, and all of Pakistan's major rivers--the Kabul, Jhelum and, Chenab--flow into it . The Indus River basin is a large, fertile alluvial plain formed by silt from the Indus . This area has been inhabited by agricultural civilizations for at least 5,000 years . </P>

What are the most fertile regions of pakistan