I presume the powder referred to is gunpowder, which was usually produced in remote locations because of the risk of explosions. This path has just crossed Powdermill Stream which it now follows to the right. Powdermill Cottage, Powdermill Lane and Powdermill Wood are not far away.
Uploaded to Geograph by Marathon on 22 June 2014
Photo © Marathon, 22 June 2014. Licensed for reuse under this Creative Commons licence