Back in 2014 I went on some hikes and took my digital camera with me.  I took pictures of things like dirt and rocks, and then later edited them to seamless and tileable.  I also made normal maps and attempted some heightmaps.  Most of these textures are 2048x2048, although a few of them are smaller.  There are 36 diffuse textures, and 88 total texture files (including diffuse, normals, and heightmaps.)

If you want full quality PNG files (almost 600MB) instead of the JPG version uploaded here (almost 150MB) you can find the PNG upload here: https://blacklodgegames.com/36-free-ground-textures-diffuse-normals-2048x2048/