Which geological features are primarily formed by erosional processes from rivers?

The formation of valleys and canyons is closely linked to erosional processes from rivers, making this the correct answer. As rivers flow, they continuously carve into the landscape through a process known as downcutting, wearing away the soil and rock along their banks. Over time, this erosional activity can lead to the development of deep valleys and canyons, which are characterized by steep sides and are often V-shaped due to the river's persistent cutting action.

While other geological features such as plateaus, ridges, mountains, and cliffs can be shaped by various geological processes, including tectonic activity or weathering, they do not primarily result from river erosion. For instance, mountains and hills are typically formed through tectonic uplift rather than direct erosion by rivers. Similarly, plateaus and ridges can be the result of volcanic activity or sediment deposition, rather than the direct sculpting caused by flowing water. Cliffs and slopes may sometimes develop from erosion, but they are not exclusively formed by river activity and can also be influenced by coastal processes or land-use changes. This distinction helps clarify why valleys and canyons specifically categorize as the features primarily shaped by river erosion.