Having heard reports of a river of concrete, I had lowered my expectations to a solid smear of grout crusting the green hill.

I was way off.

What we found bore more resemblance to a minor avalanche of concrete, which our GPS measure showed stretched more than 400 metres downhill.

To make its descent it had swamped smaller trees, flooding around rocks and logs along its path.

Cascading down the hill like a miniature glacier, the set overflow looks pretty similar to a thick coating of marzipan on the forest floor.

It's impossible to know how many plants, holes, gaps and even animals may lay beneath the stony substance.

Beneath heavy steps it would occasionally crack, crusting away and leaving everything with a chalky, industrial residue.

Underfoot, it has a similar feel to a synthetic tennis court but it moves and expands like a waterway.

In places, it's barely the width of a narrow garden path.

At others, it could pass for a single-car garage slab that nobody bothered to level.

Grooves and curves in the grout betray the substance's former liquid state and hint at the sheer speed it must have gathered as it raced down the slope.

Given how dusty it was at points, it's not hard to imagine waters from a heavy downpour carrying broken-up bits down the mountain with them.

A long way from the beaten path, the concrete river is a genuine surprise when you happen upon it.

But it certainly leaves no doubt that a lot of grout has ended up in the wrong place.