Epping Forest is an area of ancient woodland in south-east England, straddling the border between north-east Greater London and Essex. Formed in approximately 8000 BC after the last ice age, it covers nearly 6,000 acres (24 km2) and contains areas of grassland, heath, rivers, bogs and ponds. Stretching between Forest Gate in the south and Epping in the north, Epping Forest is approximately 18 km long in the north-south direction, but no more than 4 km from east to west at its widest point, and in most places considerably narrower. The forest lies on a ridge between the valleys of the rivers Lea and Roding; its elevation and consequent thin soil historically made it unsuitable for agriculture. Embankments of two Iron Age camps – Loughton Camp and Ambresbury Banks – can be found hidden in the woodland. It gives its name to the Epping Forest local government district.