The raw textures here were created and used to make 512px tiling textures, also included. (There are fewer tiles than raw textures: see what you can make of the raw materials!)
The tiled, 512px terrain textures were originally created as mapmaking resources for the oldschool Bungie games Myth, Myth II, and (non-Bungie) Myth III. My hope is that they can be used for many other things as well.
Our mapmaking guild was called bloody mud, and was active from 2001-2005. All our mapmaking resources were created from scratch. Because Myth III in particular blended textures together, our textures were often a bit higher in contrast than others you may find, so as to bring out clear detail in a lower-res game.
This set is one of several Terrain Texture sets planned for submission. See also:
http://opengameart.org/content/terrain-textures-01a-vegetation-and-humus-tiled-512px
http://opengameart.org/content/terrain-textures-01b-vegetation-and-humus-raw-sources-for-adaptation
Textures of each terrain type are similar in character and nature, because they were intended to blend and provide slight visual variety in harmony with one-another, rather than clash with one-another.
Although these resources were developed for other purposes, all my prior work is now being channeled into a CC BY-SA worldbuilding project called Vessel. Thus this project is included in my Attribution request, along with my name.