Here's why:

* Composition: Mars is a terrestrial planet, meaning it's primarily composed of rock and metal. The surface is made up of various types of rocks, including basalt, andesite, and sedimentary rocks.

* Landforms: The surface of Mars features numerous geological features, like volcanoes, canyons, craters, and plains, all of which are formed from rock.

* Dust: While there is a lot of dust on Mars, it's composed of finely ground rock particles.

So, while the surface of Mars can be covered in dust, it's fundamentally rocky beneath.