Even the type of forest a trail travels through dictates a lot about its characteristics. Most trails are hatched through thick vegetation of many kinds, depending on their location. You can expect trails that follow rivers and creeks, and that travel through coves, to have a wet, muddy, rocky, and maybe sandy surface. Mountainside trails often follow old logging or skid road beds, which have now become singletrack, in forests of oaks, some cove hardwoods, and scattered mountain laurel and rhododendrons. Ridgetop trails are often dry and rocky, passing through laurel, Catawba rhododendron, and mixed hardwoods and pines.
All trails can have rocks and roots.
Many times though, the trails do erode and become shallow clay canyons.