From Foel Drygarn in the east to Foel Eryr in the west, the Golden Road follows the distinctive ridge of the Mynyddoedd y Preseli that dominates the landscape of this part of South West Wales. Along the ridge, rocky outcrops known as crags and tors rise above the vegetated slopes. The crags and tors were formed by weathering. Weathering involves the slow breakdown of solid rock by various physical and chemical processes. One key process is freeze-thaw activity, which happens when water freezes and thaws in the cracks in the rocks.
The Golden Road is the highest part of the Mynyddoedd y Preseli. Although this area may have been covered by ice in the past, it is likely to have been ice free during the peak of the last ice age, 25,000 to 20,000 years ago, when many other parts of Wales were covered by ice. Freeze-thaw activity would have been common as it usually occurs in and near ice-covered areas. Over time, repeated freezing and thawing leads to the expansion and contraction of the cracks. This contributes to the slow crumbling of more solid rock. When entire sections of rock break off, this is known as frost shattering. These processes can lead to the formation of the crags and tors we see today.
The Mynyddoedd y Preseli have been shown to be the source of some of the stones in Stonehenge. The bluestones, spotted dolerite and rhyolite, were quarried from nearby Carn Goedog and Craig Rhos-y-felin, respectively.