Abstract

The Rainbow Imports landslide, near the mouth of Ogden Canyon in Ogden City, provides a window for viewing the subsurface conditions and movement mechanisms within the Ogden River landslide complex. The Rainbow Imports landslide scarps expose 20 to 100 feet (6 to 30 m) of unconsolidated material. We delineate four distinct landslide domains within the Ogden River landslide complex based on topography, ground-water conditions, and soil deposits. The easternmost domain is the frontage trough. Two other landslide domains, which form topographic reentrants, are the eastern amphitheater and the western amphitheater. The fourth domain, the Rainbow Imports landslide, forms a gully-like depression along the eastern margin of the eastern amphitheater.

We relate soil movement mechanisms to site conditions within the Rainbow Imports landslide area and delineate zones accordingly. The soil movement mechanisms include undercutting, earth flows, erosion, and deposition. We examine the other landslide domains within the Ogden River landslide complex with respect to the conditions and mechanisms identified for the Rainbow Imports landslide. Erosion, undercutting, and the occurrence of deltaic and lacustrine deposits is common to all the landslide domains. The topography, the thickness of deltaic deposits overlying the lacustrine deposits, and the groundwater elevations are the most variable conditions.

The effect of earthquakes on soil movement mechanisms within the Ogden River landslide complex is unknown and should be investigated.