Abstract: Ya'an to Lugu expressway is a part of the Beijing to Kunming expressway. The Lama stream is spanned by the Lama Stream Bridge along the Ya'an to Lugu expressway. To investigate engineering geological conditions at the bridge, a geological survey and field reconnaissance were conducted prior to the bridge construction. It was found that the geo-environmental conditions near and around the planned bridge site were very complicated. The so-called Xigeda strata have low strength and collapsing characteristics, which can be strongly affected by water. Under the action of water and geological structure, landslide can easily occur in slopes comprising the Xigeda strata. Base on the ground investigations at the Wenwu slope on the Lama stream along the Ya'an to Lugu expressway, this paper presents the engineering geologic and hydrogeological conditions of the landslides comprising the Xigeda strata. The paper gives results on the properties of Xigeda strata, the geological structure and groundwater. It analyzes the causes and contributing factors, finds the optimal slope gradients, the optimal slope shapes, the angle and height of slopes sensitive to landslide. It grades the dangerous degrees according to angle of slope. It provides a basis for further evaluation of slope stability. Finally, it presents some reasonable reinforcements, fill and compression and drainage measures adaptable to the geological conditions.