More on stripes, grooves and gullies

This is from the narrative of the recent NOVA film:

http://www.pbs.org/wgbh/nova/ancient/secrets-stonehenge.html

NARRATOR: Parker Pearson had discovered traces of an ancient belief system etched into the landscape around Stonehenge. But one question still lingered about the monument's location: why was Stonehenge built on such an unremarkable patch of countryside, not on a ridge or hilltop?

The answer may lie hidden beneath the surface of the Stonehenge avenue, the great processional route leading to the river Avon. This feature was mapped by running a small electric current through the soil and measuring its resistance. The technique can detect structures under the surface.

It picked up a series of mysterious grooves running beneath the avenue, for more than 200 yards. Parker Pearson was convinced these grooves were the remains of a manmade structure, older than the avenue.

His team opened a shallow trench to investigate.

MIKE PARKER PEARSON: I was convinced we were going to find evidence for gullies that contained vertical timber posts, something like that, and I was bitterly disappointed, because they were entirely natural.

NARRATOR: Soil specialists determined that these grooves were formed between two natural ridges in the landscape. During the last Ice Age, these ridges funneled rainwater and snowmelt between them. Yearly freezing and thawing caused the ground to crack into long deep grooves.

What makes the grooves extraordinary is that they are aligned with the solstices. On the winter solstice, they would have pointed directly at the spot where the setting sun touches the horizon.

CLIVE RUGGLES: Think about this coincidence in the landscape, the fact that you've got these natural stripes in the landscape actually aligning with the direction where the midwinter sun goes down. Yes, to us, it's a coincidence of nature, but imagine how that seemed to people whose mindset was different. It would have made it a very sacred and powerful spot. And that, for me, provides a very plausible reason why Stonehenge was constructed where it was.

NARRATOR: Prehistoric people built Stonehenge just beyond where the grooves end. Later, they enhanced the natural ridges with massive banks and extended the avenue all the way to the River Avon. Or so it was assumed.