Radio-carbon dating has indicated that, prior to 3800 BCE, the Peruvian desert north of Lima ( 12?S latitude ) received more seasonal precipitation and was mostly vegetated and lomas-- isolated fog oases-- existed only south of Lima.
22.
Fed by melting snows from the northern and eastern mountains and by the more evenly distributed seasonal precipitation of that area, its flow does not have the extreme variations characteristic of nearly all other rivers in the country.
