The Wye Valley Area of Outstanding Natural Beauty (AONB; Dyffryn Gwy) is an internationally important protected landscape straddling the border between England and Wales.
The River Wye (Afon Gwy) is the fourth-longest river in the United Kingdom. The upper part passes through Rhayader, Builth Wells and Hay-on-Wye, but the area designated as an AONB covers surrounding a stretch lower down the river, from just south of Hereford to Chepstow.
This area covers parts of the counties of Gloucestershire, Herefordshire and Monmouthshire, and is recognised in particular for its limestone gorge scenery and dense native woodlands, as well as its wildlife, archaeological and industrial remains. It is also historically important as one of the birthplaces of the modern tourism industry. The area is predominantly rural, and many people make a living from tourism, agriculture or forestry. Ross-on-Wye is the only town within the AONB itself, but Hereford, Monmouth, Coleford and Chepstow lie just outside its boundaries.
The varied landscapes of the Wye Valley can be explained by underlying rocks and structures, and how ice and then the river and tributary streams have acted upon them through time.
Close to Hereford, the geology of the area around the village of Woolhope is largely made up of Silurian limestones, shales and sandstones. To the south of this, the Herefordshire lowlands are largely underlain by red mudstones and sandstones, producing a redder soil. These rocks are softer than the limestones elsewhere, so the river created more meanders, a wider floodplain, and a gentler and more rolling landscape. Around Symonds Yat, limestones and red sandstones meet. This leads to a landscape of hills and plains, as well as substantial meanders which have formed impressive river cliffs.
The Lower Wye landscape was formed by the river acting on a series of layers of rock that dip towards the Forest of Dean. Here the river has incised into the margins of the Old Red Sandstone plateau to form a gorge with substantial river cliffs.