The magnitude M 6.5 earthquake on 18 June 1994 centred about 20 km southwest of Arthurs Pass, caused considerable damage to State Highway 73 through Arthurs Pass National Park, closing the highway for several days and restricting traffic for more than a week. The most serious damage occurred in the Upper Otira Gorge where a large (5-10,000 m3) rock slide covered the road and partially dammed the Otira River. Other damage affecting the highway consisted of debris and rockfalls, and slumping along the edge of poorly compacted fills. Bridges and other structures were not damaged. Damage to the highway appears to be associated with site specific factors rather than proximity to the epicentre. The pattern of ground damage may be due to the effects of topography on the propagation of earthquake waves, and variations in rock mass quality and destressing of valley slopes.