Interim Geologic Map of the West Part of - Utah Geological Survey

(Tbhv) and Dakota (Kd and Ktd) Formations, and to a lesser extent the LimerockCanyon Formation (Tl), and are several square miles in size; undivided as toinferred age because new research shows that even landslides having subduedmorphology (suggesting that they are older, weathered, and have not experiencedrecent large-scale movement) may continue to exhibit slow creep or are capableof renewed movement if stability thresholds are exceeded (Ashland, 2003); Lundand others (2009) reported on a rock fall associated with the large landslide inCedar Canyon where State Highway 14 crosses the upper part of the DakotaFormation; Qmsh denotes landslides known to be active in historical time, but anylandslide deposit may have been historically active even if not so identified; largerotational slump blocks of Isom Formation (Qms[Ti]) and Leach CanyonFormation (Qms[Tql]) are mapped in the Yankee Meadows graben and in thelower part of the Lowder Creek basin, and slump blocks of Dakota Formation(Qms[Kd]) are mapped in Cedar Canyon; query indicates areas of unusualmorphology that may be due to landsliding; thickness highly variable, buttypically several tens of feet or more thick and the largest landslides, for exampleat Yankee Meadows graben, may be as much as 600 feet (200 m) thick(Maldonado and others, 1997).Dense forests and widespread colluvium may conceal unmappedlandslides, and more detailed imaging techniques such as LiDAR may show thatmany slopes, particularly those developed on the Brian Head (Tbhv), Bear Valley(Tbv), and Limekiln Knoll (Tl) Formations and on Upper Cretaceous strata hostsurficial deposits that reveal evidence of creep or shallow landsliding.Understanding the location, age, and stability of landslides, and of slopes that mayhost as-yet unrecognized landslides, requires detailed geotechnical investigations.QmtTalus (Holocene and upper Pleistocene) − Poorly sorted, angular cobbles andboulders and finer-grained interstitial sediment deposited principally by rock fallon or at the base of steep slopes; talus that is part of large landslide complexes isnot mapped separately; talus is common at the base of steep slopes across the maparea, but is only mapped where it conceals contacts or forms broad aprons belowcliffs of resistant bedrock units; typically less than 30 feet (9 m) thick.Mixed-environment depositsQac Alluvium and colluvium (Holocene and upper Pleistocene) − Poorly tomoderately sorted, generally poorly stratified, clay- to boulder-size, locallyderived sediment deposited in swales and small drainages by fluvial, slope-wash,and creep processes; generally less than 20 feet (6 m) thick.Qaco Older alluvium and colluvium (upper Pleistocene?) − Similar to mixed alluviumand colluvium (Qac), but forms incised, isolated remnants, typically in the upperreaches of streams that drain the map area; probably about 20 to 30 feet (6-9 m)thick.QacfColluvium and fan alluvium (Holocene and upper Pleistocene?) − Poorly tomoderately sorted, non-stratified, clay- to boulder-size sediment deposited8