ABSTRACT: The stability of the slopes along a portion of the Kastraki Reservoir under static loading conditions is evaluated. The predominant geological feature in this part of the reservoir is a large plunging symmetrical syncline. Numerous clayey bedding seams with slicken sides are present within the siltstone in the syncline. It is believed that these clayey bedding seams form potential sliding surfaces resulting in a high active wedge on the western limb of the syncline pushing against a low-angle wedge on the eastern limb of the syncline. In-situ and laboratory direct shear tests were performed to determine the shear strength of the clayey bedding seams. Residual strength parameters obtained from these tests were utilized in slope stability analyses. Results of the analyses are discussed. INTRODUCTION It is generally recognized that one of the most catastrophic of all landslides involves a rock slide, consisting of a sudden, rapid slide of bedrock along planes of weakness. There are numerous examples in the literature concerning such rock slides. One such rock slide reported in the literature (Leet & Judson, 1971) occurred in 1925 on the flanks of Sheep Mountain, along the GrosVentre River in northwestern Wyoming. An estimated 37 million m³ of rock and debris plunged down the valley wall forming adebris dam about 75 m high across the river valley. The damned-up river created a lake almost 8 km long. Spring floods, two years later, resulted in the overtopping and breaching of the debris dam, claiming several lives in a town in the valley below. According to Leet and Judson, the landslide had occurred when the sandstone overlying a thin layer of clay was unable to hold its position on the clay bed during a period of heavy rain in the spring of 1925.