Remains of a pit working is confirmed by the listing by the Coal Authority and local archaeological surveys.

The area features some of the finest preserved early modern coal workings in the entire country, and each of these bumps you see are old spoil heaps or pits from around 4 centuries ago.

Each of these pits were part of the Riding Field Way - a waggonway network from the 17th century owned by Ralph Harding, which connected a ton of these very concentrated workings down to the river at the gut of the Teams. It lasted into the 18th century, when the Grand Allies took on most (or all) of it until 1844. From there use terminated, as coal production shifted southwards.

These pits were loosely organised, but probably had a central mothership facility which sorted and transported the coal. However, anything beyond this is a total guess and would need deeper research. It's still absolutely staggering, and if you're into your mining history I'd thoroughly recommend traipsing the hills south of Whickham to see for yourself.