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l'\:l C> CJl to SCALE 1150,000 LEGEND m = Irrigated I 'n ! (1965) . = Potentially Arable Land N Fil!;ure 1.7, Irrigated and put.l~ntial1y arable land in the Price River Basin (Utah Division of Water Resources 1975), salt contribution from irrigation range from about 6 percent, or 15,000 tons per year, by Hyatt et a1. (1970) to about 33 percent, or 80,000 tons per year by Gifford et al. (1975). Ponce (1975) conducted an intensive field investigation of salt pickup by over- land flows crossing Mancos Shale wildlands. Overland runoff was generated at several geologic locations in attempts to quantify salt movement, erosion, <,lod loading rates. Spatial heterogeneit'y, however, was so extreme that the results are inconclusive. His best hypothesis was that salt pickup can be described as a function of dilution (added water increasing transport capacity), erosion (separation of sediment particles from natural formations), dissolution (separation of the salt ions from the sediment parti- cles), and an interaction of the three. He fit six empirical salt uptake equations to the observed data and achieved the best correlation (r2 = 0.64) with the function: I TDSt ~ Bo + B1P - BrQs in which (1.17) of the Predicted salinity surface runoff = Precipitation rate Surface runoff rate BI, and Br = Constants TDSt P Qs Bo, Ponce (1975) concluded that the salt load that occurs with surface runoff is largely related to erosion. His quantitative analysis indicated that surface salt loading is not a unique function of rainfall in- tensity but also depends on many other unspecified factors. He also estimated that only 0.5 percent of the total salt loading at woodside can be attributed to overland flow from natural areas. Whitmore (1976) sampled Mancos Shale at nine different sites within the Price River valley. Based on laboratory analyses of these samples, he proposed that salt dissolu- tion is diffusion controlled and that two distinct dissolution rates occur. One is a fast reaction in which 80 to 90 percent of the available salt is released from the shale surface within the first 2 minutes after runoff across it begins. A second slower reaction occurs as the remaining salt slowly goes into solution. The fast rates are attributed to indigenous salt on particles at the surface of the soil, and the slow rates are thought to reflect mineral weathering. White (1977a) examined salt production from microchannels in the Price River valley. He documented the extreme surface mineral heterogeneity of the channels and described the salinity uptake in the channels as a rapid dissolution of surface salts followed 9