Mike Pitts raise some of the questions about the lines we can see on the ground, under it by excavation and through remote sensing within the Avenue at Stonehenge:
"....The Stonehenge Riverside project excavated grooves that run.. in the soil, and interpreted them as natural periglacial structures left over from the ice age, that – because they are aligned on the solstice axis – were partly responsible for where Stonehenge is: neolithic people saw the grooves pointing at the rising midsummer sun and thought, this is where we want to build Stonehenge!
Meanwhile, Tim Darvill and colleagues think the grooves are relatively modern wheel ruts. Their respective evidence is summarised in this diagram. Area 8 (enlarged at left) is a geophysics plot showing lines within the Avenue but not quite parallel to the ditches; these, say Darvill et al, are wheel ruts...."
I'm with Mike - I don't think there is a complete and clear picture of what the features are and how they relate. Yes there are periglacial stripes and the banks are probably enhanced natural banks and there are other ruts within the structure, what age are they? Are they simple farm cart ruts or evidence of processions or even stone movement? What is the history of the Palisade line that runs close by?
In support of the cart rut idea is the evidence of them continuing in a straightish line beyond where the Avenue bends as can be seen in the Magnetometer data (2010–11): white = −2nT, black = +3nT. (Aerial photograph: DigitalGlobe.) from The Stonehenge Hidden Landscapes Project