The nature reserve forms part of the Forest Hill to New Cross Gate railway cutting.
This is a site of importance for nature conservation as it contains probably the finest example of a rail-side wildlife habitat in London. The site consists mainly of mature scrub, grassland and a mixture of developing and mature woodland which has developed on the spoil left on completion of the London to Croydon Railway in 1839. The site contains good examples of plants one would normally associate with flora of secondary woodland. These include cow parsley (Anthriscus sylvestris), and Old Man’s beard (Clematis viticella). Garthorne Road is also thought to be part of the Great North Wood.