Local Geology
The London boroughs of Harrow and Hillingdon host two geological Sites of Special Scientific Interest: Harefield Pit (GLA 34) and Harrow Weald (GLA 18).

The entire area lies on London Clay and gravels, underlain by chalk, and has been mined extensively for both gravel and chalk. Sink holes are a common feature and a network of small rivers crosses the two boroughs and beyond. The historic towns of Harrow, Pinner, Eastcote, Ruislip and Uxbridge are relatively affluent and display a wide range of decorative stones in their buildings.

Local and National Geology Groups
Harefield Pit SSSI
Working with the London Geodiversity Partnership, Harrow and Hillingdon Geological Society is involved in the preservation of two Sites of Special Scientific Interest.
Pinner Chalk Mine
Harrow Weald SSSI
photo by Dudley Miles - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19946796