Fred,

My geology experience is limited, so I couldn't have told you more than "no, it isn't sedimentary, it is metamorphic and I *think* it is called the alligator back formation." However, this didn't seem substantial enough, so I hit up a geologist friend of mine who knows his stuff.

He sent me the following, which I think you will enjoy:

The rock at Rocky Knob is a schist, which is a metamorphic version of shale. The layered structure is called foliation, and developed from the oriented "squeezing" produced by the extreme heat and pressure that turned the shale into the schist. The sediments which were desposited, then pushed to great depth in the earth and metamorphosedto make this schist were deposited about 600 million years ago. They are much older than the Valley and Ridge rocks.

The formation is generally called the Alligator Back Formation, which is essentially the same as various other metamorphic rocks of the same chemical makeup (very aluminum, iron, potassium, silicon rich) seen throughout the Blue Ridge. These rocks were also "moved" to their present location along a large thrust fault, which separates them from the Valley and Ridge just east of Riner along Route 8. This fault extends for hundreds of miles along the Appalachians and separates the metamorphic rocks of the Blue Ridge from the younger, and unrelated, sedimentary rocks of the Valley and Ridge.

All of the big, white chunks of quartz seen in the fields are veins which formed in cracks within the schist after it was metamorphosed. These are common on the Blue Ridge, and entered cracks within the Blue Ridge rocks during the motion of the thrust fault mentioned above.

It's also essential to remember that the landscape we see today is the result of a couple hundred million years of erosion. All rocks seen at the surface have been exposed by-literally-miles of erosion. The result of this is hard rocks forming mountains, and soft rocks forming valleys, as seen in the valley and ridge and at various locations in the Piedmont, such as Pilot Mountain and Hanging Rock. Bull Mountain, in Patrick county, is another example.  

The interesting exception to the rule is the Blue Ridge Escarpment, which is, of course, the steep side off of Rocky Knob to the Piedmont. The escarpment is a plateau edge, and is unrelated to hard rock types. The steep slope of the escarpment is retreating as streams are diverted from the New River Valley down the steep slope to the Piedmont, producing massive erosion and pushing the steep escarpment westward. The Dan River gorge and Rock Castle Gorge are two good examples of this process. 

Rocky Knob is now at the edge of the Blue Ridge Plateau, but it would have been many miles from the edge millions of years ago. I believe it is a "Knob" for reasons of geologic structure, and the number of quartz veins in the rock. The quartz veins are very hard, and generate a framework to support the area against erosion and lowering."

And photo is clearly the Alligator Back schist. The best way to tell it is metamorphic is to look closely. You will see large, glittery mica crystals that are layered and interlocking. This indicates that they "grew" together during the heating of metamorphism. Sed. rocks can have small micas, by they are intersperesed and do not interlock. In many locations, the rocks of the Blue Ridge extend right down the escarpment and into the Piedmont-you see this just north of Rocky Knob. 

The whole area is a "cooked" (metamorphosed) deep ocean basin that formed as the Iapetus Ocean opened about 600 million years ago, give or take. Iapetus was like a "pre-Atlantic" that closed again prior to Atlantic opening. The basin was full of mud and clay; when you cook this, it makes mica-rich schists. Interestingly, the Rocky Knob stuff is probably of a similar origin to the schists we saw near Floyd, and the darker rocks around Wills Ridge. It looks a bit different (larger micas, therefore "shinier") because it was pushed a bit deeper in the crust during metamorphism and was "cooked" at higher temperature. 

Driving from Riner to the Parkway amounts to driving down into the earth, 480 million years ago (time of metamorphism; note that it is after deposition).