How can rivers form canyons across mountain ridges?

Rivers can form canyons across mountain ridges through several geological processes that allow them to maintain their paths despite rising tectonic features. While valleys typically follow the orientation of major folds and faults, transverse canyons—which cut across these structures—develop through the following mechanisms:

• Antecedence: In this scenario, a river establishes its course across a landscape before tectonic activity (such as folding or faulting) creates a mountain ridge. If the river’s rate of downcutting keeps pace with the rate at which the mountain rises, the river maintains its original path, carving a deep, transverse canyon through the emerging ridge.1
• Superimposition: This occurs when a river develops on a layer of younger sediment that buries an older, complex geologic structure. As the region undergoes vertical uplift, the river begins to entrench itself. Eventually, it is "let down" onto the underlying resistant rock, cutting a canyon across the structural trends that were previously hidden beneath the sediment.12
• Fault-controlled erosion: Rivers may also preferentially expand through existing ridges by following fault zones, where the rock is often fractured and more susceptible to accelerated headward erosion.1

In some regions, these processes may act in combination, or normal denudation may produce transverse canyons without requiring unique preexisting conditions.1