MOGBI says it's because of the mining activity. Here's another picture of the same.

Also in that area, there is a lot of holm oak woodland above Bossington. This is good for Caloptilia leucapennella. In September and October adults can be easily disturbed from leafy branches by day. There are both pale white and reddish forms. A tuft on the labial palpus gives it that snouty appearance. I've also recorded it at Minehead but am not sure how widely it occurs in the county.