The Highland Boundary Fault is a major geological feature stretching from Arran in the west to Stonehaven in the east, passing through Blairgowrie, Alyth, and Kirriemuir. Formed 400 million years ago during the collision of ancient continents, it divides Scotland into two distinct geological regions: the hard, metamorphic rocks of the Highlands to the north and the softer sedimentary rocks of Strathmore to the south. A striking feature of the fault near Alyth is Reekie Linn, a waterfall created where volcanic rocks meet sandstone, forming a 36-meter deep plunge pool and dramatic gorge. Historically, the fault also served as a cultural boundary, with the feudal system thriving south of the fault, while the rugged northern landscape fostered the clan system. This division also marked a linguistic shift from Gaelic to English, influencing Scotland’s social and cultural development.