For more detail this asset from the Unity Asset Store: Click Here
This is a paid asset, but now you can download Hand Painted Texture Pack – Natural Surfaces for FREE, Please keep in mind this package is provided only for learning purposes or to be able to test before buying the product, NOT FOR COMMERCIAL PURPOSES.
Hand Painted Texture Pack – Natural Surfaces v1.10
“If possible, please buy the package to support the developer”
This pack contains 133 highly detailed textures depicting all kinds of surfaces commonly found in natural environments. Contents: 24 Ground textures, 10 Mud textures, 8 Volcanic textures, 36 Rock textures, 19 Forest textures, 19 Grass textures, 13 Sand textures and 4 Winter textures.
All pictures come in 512×512 resolution and are fully tileable.
The set is being updated occasionally with new textures as well as new variations for existing ones.