No, mountains are not formed from the deposition of rocks and sand. While deposition plays a role in the formation of other landforms like valleys, plains, and deltas, mountains are formed through different processes.

Here are the main ways mountains form:

* Folding: The Earth's tectonic plates collide, causing the layers of rock to buckle and fold upwards. This is a common way for mountains like the Himalayas to form.

* Faulting: When tectonic plates move past each other, they can create breaks or faults in the Earth's crust. These faults can cause blocks of rock to be uplifted, forming mountains like the Sierra Nevada.

* Volcanic Activity: Volcanoes erupt and deposit layers of lava and ash, which can eventually build up into mountains like Mount Fuji.

Deposition is the process by which rocks and sand are laid down in a new location by wind, water, or ice. This process is more likely to create flat landforms like deserts, plains, and river deltas.