A Major Landslide Involving an Inverted Paleochannel in Sierra County, New Mexico

A landslide that probably dates to the end of the Pleistocene has been found in Sierra County. The feature consists of three sub-parallel segments, covering an area about 8 km wide and 10 km long. The head of the slide deposits consists of a northeast-trending paleochannel forming an inverted topography. The paleochannel deposits contain many boulders with sizes up to 1.5 meter diameter, indicating flow rate as high as 100 m3/s. The paleochannel ridge is mostly underlain by the hidden lateral contact of the Cretaceous Crevasse Canyon Formation and by the Tertiary Love Ranch and is sharply defined by Yoast Draw valley that cuts a water gap through the 25 m high inverted ridge. The landslide body consists of Love Ranch Formation overlain by a substantial cover of Quaternary fanglomerate. A series of northwest-trending faults have influenced the landslide. The broad western upslope segment of the slide has been washed away, leaving only trace evidence of a landslide. A low slide plane angle of less than 1% slope suggests a seismic trigger.