The City of Edmonton is underlaid by a thick sequence of Quatenary glacial deposits overlying gently dipping late Cretaceous clastic sediments. The Quaternary stratigraphy consists of Saskatchewan gravels and sands, two continental till deposits (upper and lower till) separated in places by Tofield sand, all overlaid by Glacial Lake Edmonton sediments. Underground activity has centered on tunneling for sanitary and storm sewer systems and, more recently, for part of Edmonton’s Light Rapid Transit system. Nearly all tunneling is in the competent till or bedrock. Other underground activity took place around the turn of the century when coal mining shafts and adits were constructed. Surface subsidence continues today and has to be considered when planning. The greatest hazard in the development of Edmonton is natural landslides that occur along river banks and man-made slopes. Major failures take place mainly in bedrock with small slips in the Lake Edmonton sediments.