Which geographic feature is formed by tectonic activity?

Mountains are formed by tectonic activity due to the movements of the Earth's lithospheric plates. This process can occur through various mechanisms, including the collision of plates, which results in the folding and faulting of the Earth's crust, leading to the uplift of land and the formation of mountain ranges. For example, the Himalayas were formed by the collision of the Indian and Eurasian plates.

In contrast, plains are generally formed through erosion and sediment deposition rather than tectonic forces. River deltas are created at the mouths of rivers where sediment is deposited as the river flows into a larger body of water, not through tectonic events. Deserts, while they can be influenced by geological features, primarily result from climatic conditions such as low precipitation rather than direct tectonic activity. Therefore, mountains are distinctly recognized as geographic features directly resulting from tectonic forces.