Engineers burying power lines in the Yorkshire Dales have unearthed a piece of ancient history which has baffled local experts.

The strip of ash and burnt material was discovered in Kingsdale, near Ingleton, by an archaeologist working for United Utilities and Electricity North West.

Arthur Batty, of Ingleborough Archaeology Group, initially thought the find was a fire pit – a temporary hearth used by nomadic hunter-gatherers. But it is the wrong shape and depth and no-one has yet been able to shed further light on it.

Arthur said: “We have had the feature carbon-dated and it is Iron Age, about 300BC. Previous finds in Kingsdale have given evidence of human activity from 6,700BC, but we have very little from this particular Iron Age era so it’s quite a significant find.”

Engineers alerted Arthur, who was brought up in Kingsdale, after spotting changes in soil colour while digging trenches for cables.

Around five kilometres of overhead power lines and poles in Kingsdale are being replaced with underground cable as part of a project to improve the view. The scheme is funded by Electricity North West and is being carried out by United Utilities.

“There is plenty of evidence of prehistoric fire pits and hearths in Kingsdale, but this find is different,” said Arthur. “It is a long feature and buried about 800mm below ground whereas you would expect a fire pit to be roughly circular.

“Geophysical survey shows other adjacent anomalies at a similar depth, which could be a cluster of hearths. There is also some stonework and paving less than 50m away in the river bank which is being eroded away. This could date to around the same period. More surveys are proposed.

“It raises a lot of questions that only more detailed research could possibly answer, but it is a very tantalising glimpse into the history of this beautiful area.”

United Utilities project manager Eamon Robinson said: “We try to plan cable routes to avoid historical areas, but sometimes things crop up you just can’t expect. That’s why we quite often employ archaeologists to look over our shoulders.

“We have now almost finished laying cables and expect to be able to remove poles and wires early in the new year, meaning visitors will be able to enjoy uninterrupted views of the valley for the first time in many years.”

Arthur is co-author of a book called The Kingsdale Project, about the discovery of a fire pit dating back to 6,700BC. For more information visit ingleborougharchaeologygroup.org.uk