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Francis J. McCarthy III
James P. Dobrowolski
Abstract-Recent concerns over the quality of water delivered to domestic wells in Rush Valley have prompted an interest in water yields from tributary watersheds. Removal of juniper trees
(Juniperus osteosperma) by wildfire and prescribed burning has altered the hydrologic regime of these small watersheds. The saturated areas and perennial springs that have emerged might offer direct benefits to humans, livestock and wildlife in the form of greater vegetation production later in the growing season and as more reliable wa ter sources. We are collecting baseline hydrogeologic data and investigating the emergence of springs. Specific objectives include the determination Qf subsurface flow paths to selected springs and computer modeling to predict potential spring occurrence. The study area near Tooele, UT, is geologically and hydrologically complex. Most of the springs appear to occur at points of subsurface flow concentration where a shallow soil mantle exists over shale, or where fractured and solution cavities in rock are exposed and these cavities are simultaneously underlain by impermeable shale.
The removal of juniper trees (Juniperus osteosperma) has altered the hydrologic regime of several small watersheds in the Johnson Pass area of Rush Valley, Utah. Large increases in spring activity and water yields were observed after wildfires and prescribed burns removed junipers from tributary watersheds. Recent concern over watershed condition and the quality of water delivered to domestic wells in Rush
Valley has prompted an interest in water yielded from upslope areas. Efforts to improve the watershed condition for wildlife and livestock, as well as the quantity and quality of the ground water within the valley, have led to the formation of the Clover Creek Coordinated Resource Management Plan (CRMP) (USDA 1997). The purpose of the
CRMP is to increase and maintain the availability and duration of surface water flows, enhance ground water recharge, increase and maintain plant diversity and structure, and provide quality habitat for wildlife and livestock.
The objectives will be met using a variety of management practices, primarily vegetation manipulation. The study area near Johnson Pass has been established by the Utah
State University Department of Rangeland Resources and the Utah Agricultural Experimental Station.
Over the past 100 years, fire suppression and overgrazing likely led to increased tree density and/or invasion of juniper trees into adjacent rangeland throughout the region (West 1989, USDA 1997). Oblique photographs from the 1880's show an area with much lower juniper tree density and aerial extent than in 1997 (fig. 1). Portions of the study area were chained and seeded with grasses in
1974 and 1975 to remove the juniper and increase forage availability. In 1991, wildfires and prescribed burning removed additional junipers, especially on the upper portions of the watershed. Following the fires, numerous seeps, wet meadows and perennial springs emerged. Riparian areas are developing within previously dry stream channels.
The purpose of this investigation is to provide baseline hydrogeological data for our study area and examine the emergence of springs. Specific objectives include the determination of subsurface flow paths to selected springs and computer modeling to predict potential spring occurrence. The Johnson Pass area is geologically and hydrologically complex (fig. 2). Several mechanisms for spring
In: Monsen, Stephen B.; Stevens, Richard, comps. 1999. Proceedings: ecology and management of pinyon-juniper communities within the Interior
West; 1997 September 15-18; Provo, UT. Proc. RMRS-P-9. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Rocky Mountain Research
Station.
Francis J. McCarthy III is Research Assistant and James P. Dobrowolski is
Associate Professor, Department of Rangeland Resources and Acting Director,
Watershed Science Unit, Utah State University, Logan, UT 84322-5230.
Figure 1Top photograph was taken in the 1880's of the southern end of the Stansbury Mountains looking north into the Big Hollow area. Note small number of junipers on lower hillslopes when compared to the bottom photograph taken in November 1996 of the southern end of the
Stansburys and northern Onaqui Mountains looking northwest into the Big Hollow and Johnson Pass areas.
194 USDA Forest Service Proceedings RMRS-P-9. 1999

Figure 2-Geologic map with the study area outlined by a black rectangle (after Croft 1956).
USDA Forest Service Proceedings RMRS-P-9. 1999
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Figure 3-(A) Subsurface flow over a soil mantle resulting in a spring where the soil pinches out. (8) Possible flow paths through confined layers or along faults overlain on part of cross section (after Croft 1956). area. The majority of the study area is underlain by the
Manning Canyon Shale. This is composed of three units: a lower black shale, a medial dark gray limestone unit and an upper black shale and quartzite unit (Rigby 1958). The shales are thin bedded and highly fissile. The shales are easily erodible and frequently buried. The medial quartzite outcrops very strongly across the study area and may be mapped as a marker bed. Quartzite layers are very hard and often have a scintillating appearance and visible cross bedding (Rigby 1958). The Oquirrh Formation outcrops strongly across the eastern side of the study area. It is primarily composed of hard, black to gray, well-bedded limestone with occasional clastic layers. Several strong structural features are evident across the area. The area is broadly warped into an anticline and syncline (fig. 3B) as part of a regional fold and thrust system. Numerous minor faults and folds occur within the area. Several periods of faulting have occurred.
Ancient thrust faults were later dissected by strike-slip faulting and finally by Basin and Range normal faulting
(Croft 1956). Muchofthethrustfaultingoccurred within the
Manning Canyon Shale making the stratigraphy hard to map due to omission or repetition oflithologic units (Rigby
1958).
The hydrology ofthe area focuses on two perennial spring fed streams, Chokecherry Creek and Serviceberry Creek.
Annual mean flows are estimated to be less than 0.14 m 3 /sec
(5 ft 3 /sec (cfs)) and the streams have historically dried up during the summer months (Darrell Johnson, personal communication 1997). Recent increases in water yields have resulted in the streams flowing all year with the creation and extension of riparian areas. Several wet meadows have appeared where springs occur outside of stream channels. emergence are possible. It is hypothesized that most of the springs occur at points of subsurface flow concentration where a shallow soil mantle exists over low permeability bedrock, such as shale, or other barrier to flow (fig. 3A)
(Watson and Burnett 1995). Alternatively, water may flow through a confined aquifer of fractured bedrock or bedrock with solution cavities. The flow might be controlled by structural features such as faults which provide preferential flow zones or fracture the area into discrete packets of infiltration transfer and discharge across the site (fig. 3B).
The study area is located in a high valley in the transition zone between the northern Onaqui Mountains and the southern Stansbury Mountains. Elevations within the study area range from 1,524 to 2,408 m (5,000 to 7,900 ft) above sea level. Relief is moderate compared to the surrounding terrain. Temperatures range from below zero in the winter to over 40°C (-20 to 100+ OF) in the summer. Precipitation averages 480 mm (19 inches) per year (USDA 1988).
Approximately 88 percent occurs as snowfall during the winter. Occasional monsoonal thunderstorms drop large amounts of precipitation on the area in short periods oftime.
Vegetation in the area consists primarily of grasses and shrubs where the junipers have been removed. Soils are thin, generally less than 50 cm (20 inches), and poorly developed (USDA 1988). Few geologic studies have been conducted in the area. Previous mapping efforts focused on larger scale structures and formations (Croft 1956). Three geologic formations are present, the Mississippian Great
Blue Limestone, the Mississippian and Pennsylvanian Manning Canyon Shale and the Pennsylvanian to Permian
Oquirrh Formation. The Great Blue Limestone consists of massive, thick bedded, medium to dark gray limestone. It is resistant to erosion and forms the western ridge of the study
The investigation consists of a two-phased approach. The first phase consists of detailed Global Positioning System
(GPS) assisted hydrologic and geologic mapping, including the construction of several piezometers to monitor potentiometric surface and map depth to bedrock. The second phase involves predicting the occurrence of springs and the potential for spring occurrence using a geographic information system and flow path analysis.
Phase I efforts consisted of detailed mapping of streams, roads, springs, geological contacts, geological data points, water troughs, and numerous other points of interest utilizing a handheld GPS to produce high resolution, high accuracy maps. These data are then spatially corrected and incorporated into a GIS. Earlier mapping data also will be incorporated into the GIS.
We are constructing stratigraphic and structural geologic maps to identify water bearing units and their orientation and lateral extent. Stratigraphic mapping consists of identifying and characterizing individual lithologic units and their vertical sequence. Geologic and structural mapping helps to determine the lateral extent and three dimensional orientation of each lithologic unit. Of special interest is the identification of folds and faults that might act as preferential flow paths. Field mapping will be supplemented by high resolution aerial photography. One to five thousand scale color infrared stereoscopic photographs will be acquired and used to assist surface mapping and the creation of high resolution digital terrain models (DTM's).
196 USDA Forest Service Proceedings RMRS-P-9. 1999

From these mapping efforts, several sites will be selected for construction of5 cm (2 inches) piezometers to determine the potentiometric surface and monitor ground water levels.
A 9.8 cm (3.87 inches) borehole will be drilled using a direct mud rotary technique. During drilling, information on soils, lithology, depth to bedrock, and depth to water will be collected and incorporated into the GIS. The piezometers will be completed with 5 cm PVC pipe with a screened interval ofl.5 to 3 m (5 to 10 ft). In areas with more than one water bearing unit nested piezometers will be screened to measure the potentiometric surface of each unit.
Phase II involves GIS modeling to attempt to determine what parameters promote spring occurrence and to use these parameters to predict current spring locations where springs might appear and to predict spring development iff when the vegetation is manipulated. Preliminary efforts used standard 30 m x 30 m (98 x 98 ftrpixel size digital terrain models to examine the flow accumulation and the curvatures of the slope profile and planform to identify possible points of concentration in the topography where springs are likely to occur. Finer resolution DTM's will be created to determine drainage area, relief, aspect, slope length, curvature, and other topographic features related to each spring occurrence. These data will then be overlain with the GIS coverages of geology, potentiometric surface, depth to bedrock, and vegetation to identify the strongest influences on spring occurrence. If used to predict spring occurrence if the vegetation is manipulated.
Preliminary Results and
Discussion
At present, results show that GPS based mapping is very efficient and rapidly converted to GIS coverages. Most ofthe data collected is still of a qualitative nature, however, several strong features can be noted. Figure 4 shows the
t
-----.~--~------.--.-.
-
=Crossection line _ Wet meadows , Spring Fault
Streams ~.' Middle Gray Limestone of Manning Canyon Fm.
Figure 4-Geographic Information System (GIS) based map of a portion oftheChokecherry
Creek tributary watershed.
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197

198 locations of springs, saturated areas, streams, watershed boundaries, roads, geological contacts, and outcrop locations. Only the distinct contacts between the Manning
Canyon Shale upper and lower units and the medial limestone, and the contact between the Manning Canyon Shale and the Oquirrh Formation were mapped using the GPS.
Numerous strike and dip points represented by the triangles were taken to determine the orientation of the lithology. The stratigraphy is interrupted by several faults and folds within the area making stratigraphic mapping difficult. However, by focusing on the shale-limestone contacts, it is possible to get a general picture of the structure and lateral extent of lithologic units. Springs mostly appear along the contact of the shales and limestones, especially where the Manning Canyon Shale contacts the Oquirrh
Formation.
The most apparent features mapped-are the wet meadows and other saturated areas. Several hectares of saturated soil are apparent all year. The limited infiltration of these areas from high antecedent moisture levels, might lead to greater runoff and a concomitant increase in hydrograph storm peaks (Betson 1964, Dunne and Black 1970).
Slope instability and seepage erosion were observed in several locations across the site. Figure 5 indicates a fenced exclosure that was disturbed by failure of the slope. Strong seepage erosion appears to have undermined soil and bedrock creating spring sapping features such as streams emanating from steep semicircular slopes. Several areas across the site have similar features without flowing streams, indicating relict spring sapping features. These may provide additional insight to subsurface water flow in the area and might be incorporated into the predictive model.
Initial stratigraphic mapping shows that the Great Blue
Limestone contains abundant solution cavities which might act as an aquifer, however, few spring occurrences were observed in the formation. The Manning Canyon Shale is generally impervious, although some areas are highly fractured and have open calcite lined fractures capable of moving water (Arthur 1961). The quartzite within the Manning
Canyon Shale often contains open fractures that also may act as conduits for flow. Whether the medial limestone acts
Figure 5-Active seepage erosion occurring in one of the tributary watersheds.
Figure 6-Potential spring occurrence sites shown in grey-white based on slope curvature and flow accumulation. Actual springs are in black at 30 x 30 m (98 x 98 ft) pixel sizes.
N t as an aquifer or barrier to flow has yet to be fully determined.
Many of the springs appear to emanate below this unit.
Manning Canyon Shale medial limestone outcrop patterns suggest that numerous smaller folds exist across the area, as well as several unmapped faults. Detailed mapping should reveal continuation of previously mapped faults through the shale. These faults and folds might be important in controlling the behavior of many ofthe springs in the area.
These structures might result in separate discrete zones of infiltration, transfer, and discharge with much ofthe transfer and discharge occurring along faults or areas where deeper soils pinch out. Movement through the soil mantle is likely, however, mapping suggests soils are too shallow and too laterally discontinuous to provide continuous flow paths. The geology of the site appears to inhibit deep penetration of ground water. Small changes in the water budget due to vegetation manipulation or climate change should be readily visible in the stream and springs.
Initial efforts to model the flow accumulation and curvature of the slopes using low resolution (30 m, 98 ft) DTM's to identify zones of flow concentration where springs might occur indicated poor results (fig. 6). Most spring features are smaller than 30 m and are obscured by the grid. Higher resolution DTM's (2 m, 6 ft) should provide enough detail to parameterize the area.
Conclusions
Preliminary results indicate that most subsurface flow is through fractured bedrock and that the structure might create discrete packets ofinfiltration, transfer and discharge across the site. Depth to bedrock, depth to water, and the potentiometric surface will be important to determining the flow paths to springs. The removal of juniper trees in this area increased water yields though there are a few negative side effects such as slope instability and seepage erosion. Further, the unique geology of the site forces ground water to the surface, allowing gains in water yield to be readily
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exploitable. Initial modeling efforts are at too coarse a scale for adequate predictive modeling. Higher resolution DTM's are required to examine spring sapping and other topographic features related to modeling at our site.
Acknowledgments
Special appreciation to Darrell Johnson and family for field assistance, a verbal history of the study area, and use of their private land. Norm Evenstad and Carlos Garcia of the NRCS for technical reports, aerial photographs, and information.
References
Arthur, W. J. 1961. Unusual solution cavities in the Manning
Canyon Shale near Fairfield, Utah Geol. Soc. Am. Bull. 72:
767-768.
Betson, R. P. 1964. What is watershed runoff? J. Geophysical Res.
69: 1541-1552.
Croft, M. 1956. The geology of the Northern Onaqui Mountains,
Unpublished M.S. Thesis, Brigham Young University, Provo, UT.
Dunne, T. and R. D. Black. 1970. Partial area contribution to storm runoff in a small New England watershed. Water Resour. Res. 6:
1296-1311.
Rigby, J. K. 1958. Geology of the Stansbury Mountains, Tooele
County, Utah. Guidebook to the Geology of Utah no. 13, Utah
Geological Society, Salt Lake City, UT.
United States Department of Agriculture, Soil Conservation Service and Forest Service. 1988. Shambip River Basin Study,
USDA, Salt Lake City, UT.
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