Compared to newer 3D games, where models are fully textured, Mario’s model in Super Mario 64 has only five textured areas: his eyes, his mustache, his sideburns, the buttons on his overalls, and the M on his cap. The rest of the model is surfaces filled with a solid color by the game’s engine. Here is Mario’s model without the textures.
In Super Mario 64, you might notice a seam in the quicksand around the middle of the stone walkways in Shifting Sand Land. The reason for the seam is that the game can only handle rectangular liquid surfaces, so all water, lava and quicksand areas that are irregularly-shaped need to be subdivided into rectangular parts. The second picture is Shifting Sand Land seen from below, showing how the quicksand is broken up.