Field trip no. 11 from “Geologic Excursions to the Rocky Mountains and Beyond,” field trip guidebook of the 1996 Annual Meeting of the Geological Society of America. (SP-44 has the complete set.) 21 pages. Digital PDF download. OF-96-04-11D
From the Introduction:
This field trip to examine the kinematics of the Slumgullion landslide (Fig. 1) provides an opportunity to examine structural features produced by the movement of the landslide. Part of the landslide has been observed to be actively moving for at least the past 100 years, and features on the landslide surface are continuously created and destroyed by the movement. The structural features that we can observe are along the active margins and within the body of the active landslide. Faults and fault zones are typical features along the active margins. The landslide flanks are characterized by strike-slip faults. Normal faults are typical of the uppermost parts of the landslide, and thrust faults are typical of the distal parts of the landslide. Within the body of the active landslide, structural features are produced by a change in the boundary geometry or by variations in the velocity of movement. The resulting deformation is characterized by stretching, shortening, and shearing.
By virtue of its great size, the Slumgullion landslide contains many different examples of deformational responses to continuous movement. The understanding of a large structural feature within the landslide begins with the observation of tiny fractures that serve as guides to deformation. The guide fractures can be interpreted in the context of expectable deformation in different parts of the landslide. Aggregates of guide features allow the interpretation of structures. During this field trip we will make a traverse down the active landslide to observe these various guide features and show how information from them is used in the interpretation of structures. We will also see some structures, notably clay intrusions and extrusions and flank ridges, which are still poorly understood. In this traverse, we will see places where clay has been intruded along shear zones and places within the body of the landslide where it has extruded onto the ground surface.