Halkyn Common and Holywell Grasslands (Welsh: Comin Helygain a Glaswelltiroedd Treffynnon) is a Site of Special Scientific Interest (SSSI) in Flintshire, north Wales covering Halkyn Mountain and surrounding areas. Lying 4 km (2.5 mi) northwest of Mold on a plateau about 100–300 m (328–984 ft) above sea-level, it occupies an area of 699.3 ha (1,728.0 acres) comprising grassland, heathland, and numerous spoil tips and quarries, relics of its industrial past.[1]
The relict industrial landscape supports the largest areas of calaminarian grasslandGrassland growing on soil containing high levels of heavy metals. in Wales.[1]