How to make a texture fade from one to another (Landscape)

I’m building a landscape for school and want to have a mountain texture fade to a grass texture. I need the simplest way to do it if anybody knows that would be awesome, thank you.

The CGCookie Island tutorial has that:

He does texture blending starting around the 10min mark. It’s Blender Internal, but I think it’s possible to do the same thing in cycles.

Terrain blending is easy in Cycles compared to BI, you just need to geometry node and string the normal coordinates through a normal node and a vector map node, once you do that, you will be able to get a mask that you can use to texture your terrain based on slope.

To do the same in BI means creating a special light group along with a mask material that uses it. Then you create your terrain materials (which is lit only by the normal light setup), and use nodes to blend them together based on the mask. A little more complicated, but still possible.

In Blender Internal you can just insert mask in-between two textures, and set it as stencil via checkbox at the bottom of the Influence sub-panel. Black areas of the mask are where preceeding texture shows up, white areas are where succeeding texture shows up.