series of ranges in southern Andhra Pradesh state, southern India. The hills trend northwest to southeast and form the central part of the Eastern Ghats. Geologically, they are relicts of ancient mountains formed during the Cambrian Period (about 540 to 490 million years ago) that were subsequently eroded by the Penneru River and its tributaries. The Punchu and Cheyyeru rivers join in a spectacular confluence in a gorge in the corridor between the Velikonda Range and the Palkonda Hills. Formed of quartzites, slates, and lavas, the Palkondas reach an elevation of about 3,000 feet (900 metres) in the south. The valleys between the mountains are drained by streams, many of which, having been dammed for water-storage tanks, provide irrigation for cultivation. The main crops are jowar (grain sorghum) and peanuts (groundnuts).