The Highland Boundary Fault is a major fault zone that traverses Scotland from Arran and Helensburgh on the west coast to Stonehaven in the east. It separates two different geological terranes which give rise to two distinct physiographic terrains: the Highlands and the Lowlands, and in most places it is recognisable as a change in topography. Where rivers cross the fault, they often pass through gorges, and the associated waterfalls can be a barrier to salmon migration.

The Isle of Arran or simply Arran is an island off the west coast of Scotland. It is the largest island in the Firth of Clyde and the seventh-largest Scottish island, at 432 square kilometres (167 sq mi). Historically part of Buteshire, it is in the unitary council area of North Ayrshire. In the 2011 census it had a resident population of 4,629. Though culturally and physically similar to the Hebrides, it is separated from them by the Kintyre peninsula. Often referred to as "Scotland in Miniature", the Island is divided into highland and lowland areas by the Highland Boundary Fault and has been described as a "geologist's paradise".