NBMG Report 53

Geologic Assessment of Piedmont and Playa Flood Hazards in the Ivanpah Valley Area,
Clark County, Nevada

P. Kyle House¹, Brenda J. Buck², Alan R. Ramelli¹

¹Nevada Bureau of Mines and Geology, University of Nevada, Reno
²Department of Geoscience, University of Nevada Las Vegas

2010

 

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List of Figures

 

Frontispiece. Southern edge of Jean Dry Lake, looking south.

Figure 1. Shaded relief map of Ivanpah Valley study area (colored) showing 7.5’ quadrangle maps and playa watersheds (blue: Roach; green: Jean; peach: Hidden Valley; pink: Ivanpah). The shaded relief is based on 30-m digital elevation data from USGS.

Figure 2. Individual playa drainage areas as percentages of study.

Figure 3. Oblique aerial view of the southern part of the Ivanpah Valley study area. Photographer in airplane situated over the Spring Mountains looking SSE. Roach Playa is prominent playa in center of image; Lucy Gray Mountains and McCullough Mountains in left background; Table Mountain in lower right corner. Photo courtesy of Jim Faulds, NBMG.

Figure 4. Surficial geologic map of the Ivanpah Valley area (House et al., 2006). Greatly reduced representation.

Download Surficial Geologic Map:
	Full Size Hard Copy Version (.pdf)		Google Earth Version (.kmz)		GIS Data in UTM NAD 83, ESRI Shapefile format (.zip)

 

Figure 5. Quickbird satellite imagery used in the compilation of geologic linework.

Figure 6. Generalized geologic map of study area also showing locations of recorded field observations by the authors.

Figure 7.  Examples of tributary v distributary drainage pattern, inset topographic relationships, and the the value of Quickbird imagery for interpreting geologic relations. Red box in third image indicates location of large-scale map and image.

Figure 8. Series of 4 photos that illustrate the sequence of topographic leveling that occurs over time once active alluvial surfaces are abandoned. Top left: coarse gravel bar in active channel, unit Qay₃; Bottom left: greatly subdued gravel bar crest on young abandoned surface, unit Qay₂; Top right: older, but coarser gravel bar crest on older Qay₂; Bottom right: Planar surface remnant with scattered protruding cobbles, unit Qay₁.

Figure 9. Illustration of time-dependent changes in soil carbonate horizon morphology in gravelly soils. Modified with permission from figure provided by Amy Brock.

Figure 10. Example of strong stage III carbonate soil horizon in unit Qai. Note varnished clasts on planar surface.

Figure 11. Stage IV carbonate in unit Qai. Field book for scale. Note laminar carbonate near surface.

Figure 12. Example of very strongly developed Stage VI soil carbonate horizon in unit QTa/Tay. Note prominent and thick laminar carbonate near bottom of photo.

Figure 13. Extremely strongly developed stage VI carbonate soil in unit Tek, Jean Hills area, clipboard for scale. This is an exceptionally thick and strongly developed soil carbonate horizon by any standard.

Figure 14. Examples of planar morphology and desert pavement patterns typical of unit Qay₁ and Qai. Note moderately strong desert pavement development in each example and slightly protruding gravel bar crests in lower image. Top: Qay; Middle: Qai; Bottom: Qay₁.

Figure 15. Deeply weathered limestone boulders on Qai surface. Darker, protruding areas are chert lenses and nodules that are not susceptible to chemical dissolution; Unit Qai.

Figure 16. Dissolution pits on large sandstone cobble (upper) and etched furrows on limestone clast (lower). Both examples from Qai surface.

Figure 17. Top: Moderately to darkly varnished granitic gneiss surface clasts in tight desert pavement on unit Qai, Lucy Gray fan. Overturned clast shows strongly reddened bottom surface. Lithology includes volcanics and granitic gneiss. Bottom: Example of split rock fragments on Qai surface. Predominantly granitic gneiss.

Figure 18. Variability in desert pavements in the study area. A: Qay₁ surface with abundant varnished chert and sandstone gravel; B. Qay; C. Qay₁; D. Qay₁; E. Qai; F. QTa surface with fragments of petrocalcic horizon; G. older Qai surface with calcic pendants and petrocalcic fragments; H. QTa/Tay with exposed petrocalcic horizon.

Figure 19. Simplified geologic map of the study area showing the distribution of general surficial units and bedrock types. Basin boundaries are indicated. UTM grid (NAD 83) shown with 10 km spacing.

Figure 20. Correlation of map units.

Figure 21. View looking ESE across the study area toward Sheep Mountain (foreground) and the McCullough Range (background). Hotel-casino structures typical of unit Qx in the valley are evident.

Figure 22. South-looking view from near the southern edge of Jean Playa. McCullough and Lucy Gray ranges and Sheep Mountain in the background. Photographer standing on the playa surface which, here, is characterized by widely dispersed fluvial cobbles on flat-lying muds. Light yellow band in middle ground is playa fringe area and green swath beyond is comprised of alluvial fan deposits. 

Figure 23. Automobile wreckage on Roach Playa. View looking south toward the southern end of the Spring Mountains. Clark Mountains in the distance.

Figure 24. Roach Playa fringe. This photo, looking north toward the Bird Spring Range, shows mudcracked silt from recent piedmont runoff onto the playa surface. Darker toned area just beyond the truck is veneer of gravel related to the same runoff event. Light band of vegetation beyond the playa edge marks zone of predominantly eolian deposits.

Figure 25. Fresh aeolian sand on crest of small bedrock ridge NE of Roach Playa. View toward Sheep Mountain. Note fresh ripples in sand deposit. Many bedrock outcrops in this area show clear evidence of wind-abrasion.

Figure 26. Thick aeolian deposits in the form of 'sand ramps' on the west-facing slopes of a ridge of the McCullough Mountains that encloses Hidden Valley along its western edge.

Figure 27. Typical aeolian sand sheets in the field area.

Figure 28. Typical outcrop of unit Tek.

Figure 29. Unit Qc is most common in areas of cliff-forming sedimentary rocks in the field area. This photo is from near the Bird Spring area.

Figure 30. Typical expression of unit Qcf as mapped in the study area in the Northern McCullough Mtn area. The map unit is commonly a mix of talus, colluvium, and small bouldery debris fans.

Figure 31. The active channel of Roach Wash, the principal axial drainage at the north end of Roach Lake. Fresh fluvial bedforms and bar features are obvious.

Figure 32. Boulder deposit in unit Qay₃.

Figure 33. Typical active ephemeral wash in unit Qay₃.

Figure 34. Typical Qay₂ surface showing muted but obvious depositional topography and weakly weathered surface clasts.

Figure 35. Typical distal Qay₁ surface showing flat pavement with moderately interlocking surface clasts.

Figure 36. Typical medial Qai surface remnant showing flat surface with moderate to tightly interlocking pavement and strongly weathered clasts.lat pavement with moderately interlocking surface clasts.

Figure 37. Typical Qao surface showing variably paved surface composed of abundant petrocalcic chips and darkly varnished rock fragments.

Figure 38. Eroded, ridge-like remnant of QTa showing deeply weathered clasts and retrograde pavement on moderate to steep slopes.

Figure 39. Typical outcrop and surface expression of Tay showing very strongly cemented carbonate horizon.

Figure 40. Comparison of Ivanpah Valley alluvial units to piedmont alluvial chronologies reported from proximate sites in the Mohave Desert. Providence Mountain data from McDonald et al., 2003; Spring Mountain piedmont data from: A. Bell et al., 1997, 1998; B. Sowers et al., 1988; Las Vegas 30’ x 60’, Page et al., 2005. Ages and representative durations in individual units are, in part, approximated. Geologic time scale based on USGS and ICS.

Figure 41. Relative flood hazard map of the Ivanpah Valley study area.

Download Flood Hazard Map:
	Full Size Hard Copy Version (.pdf)		Google Earth Version(.kmz)

 

Figure 42. Areal extents of the series of 1:24,000-scale flood hazard maps.

Figure 43. Simple relationship between geologic map units and relative flood hazard classes.

Figure 44. Three characterizations of The Lucy Gray alluvial fan. Upper: Quickbird® satellite image; Middle: Surficial geologic map; Lower: Relative flood hazard class map.

Figure 45. Three characterizations of the central study area. Upper: Quickbird® image mosaic; Lower: Relative flood hazard class map.

Figure 46. Top: Quickbird image; middle: geologic map; bottom: derivative flood hazard map for lower part of the Goodsprings Fan.

 

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