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alluvial valley .floors are, most likely, accumulated in and pass through these
<br />narrower valleys. Thus their disturbance may be as important as the disturbance of
<br />the actual alluvial valley floor. But those upstream areas were not mapped here.
<br />Schmidt (1977) did map the upstream wildlife areas in the area of northeastern Mon-
<br />tana he investigated.
<br />Aerial imagery was utilized to assess the relative vigor of v to in low-
<br />land areas. Relative vigor was shown in color infrared aerial c ected
<br />during the drier months since the more vigorously growing v p asized
<br />at this time. When this sign (of growth) is noted, the ~ r is also
<br />identifying areas where shallow ground water is likely t t le or soil
<br />moisture is maintained at a level high enough to sustain ation. There is
<br />no equally direct indication of tha quality of ground wate ough large differences
<br />in the.quality of ground water would be reflected by the composition of vegetation.
<br />It was not possible to assess the species included in the vegetation of sub -
<br />irrigated lowland areas using aerial imagery. Therefore, the methodology incor-
<br />porated the use of available ground level photographs and other site - specific infor-
<br />mation gathered by investigators at a number of mine sites *. Therefore the vegeta-
<br />tive data presented are neither detailed nor complete since field surveys were not
<br />performed.
<br />Alluvial valley floor designations were verified where hay cropping in the val-
<br />ley floor was observed in the aerial imagery. However, occasional difficulties were
<br />encountered in identifying alluvial valley floors. Storage reservoirs located in
<br />the alluvial valley floors may restrict the extent of downstream flooding and
<br />usually increase the subirrigated area by raising the local water table in the
<br />vicinity of the impoundment. Such uncertainties in mapping, and others that exist
<br />where irrigated lands border the alluvial valley, were not completely resolved during
<br />the investigation. However, the effects of these impediments to accurate mapping
<br />were considered trivial for the sites evaluated.
<br />The methods used here to identify alluvial valley floors are therefore largely
<br />empirical. A definition of a complex interrelationship of geologic, hydrologic,
<br />biologic, and topographic conditions that have surface, subsurface, time - related and
<br />use - related components was attempted. Since this was done without benefit of ade-
<br />quate field data, it is likely that the definition will improve as field data are
<br />compiled.
<br />It is concluded that alluvial valley floors can be mapped in the manner used
<br />here with reasonable certainty. Geological, ground water, and vegetative studies
<br />would surely refine this analysis, but such investigations would require additional
<br />time and field efforts. The reconnaissance methodology utilized for this report may
<br />remain a suitable technique for initially identifying alluvial valley floors. Fur-
<br />ther calibration with ground truth and subsurface data to confirm its accuracy would
<br />be desirable. But it is believed that the procedures used adequately identify the
<br />alluvial valley floor areas that are subirrigated. What is not identified is the
<br />hydrologic system that supports the subirrigation.
<br />* Mines for which ground -truth data were available in some form and which had been
<br />visited include Black Mesa, Rayenta, Craig, Edna, Energy (1, 2 & 3), Seneca, Colo -
<br />wyo, Absaloka, Big Sky, Circle West, Rosebud (MT), Decker, Savage, Spring Creek,
<br />Youngs Creek, Navajo, San Juan, Star Lake, Beulah, Center, Falkirk, Gascoyne, Glen -
<br />barold, Husky, Indian Read, Velva, Alton, Eagle Butte, Belle Ayr, Big Horn, Black
<br />Thunder, Coal Creek, Cordero, Dave Johnston, East Gillette, Jacobs Ranch, Jim Brid-
<br />ger, Lake DeSmet, Medicine Bow, North Rawhide, PSO Dl, Rosebud (WY), Seminoe, Soren-
<br />son, Welch, Whitney, and Wyodak (See Appendix 1 for locations).
<br />
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