This paper describes an investigation of the 1939 flow slide in colliery spoil at Cilfynydd Common, South Wales. The investigation concentrated on the geomorphological features and other aspects that were to be destroyed by a proposed reclamation scheme. The overall aim of the work was to compile a database of factual information on ground and material conditions at the flow slide site. The work involved geomorphological mapping, a site investigation which involved 18 trail pits and a detailed programme of laboratory testing including fabric analyses. The results of the study indicated distinctly different fabrics for materials from different locations in the failed mass of the landslide. In triaxial stress path tests excess pore water pressures were generated very rapidly during shearing, indicating the susceptibility of slopes formed of colliery spoil to fail by flow slide.