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<br />w <br />W <br />t . <br />.' <br /> <br />.,;;. <br /> <br />Contributions from BLJ\I-Administered Lands <br /> <br />The Bureau of Land Management administers 53 million acres of public lands in tile <br />Colorado River basin above Yuma, Arizona. and 48 million acres above Imperial Dam. <br />about 40 percent of the basin's total area Approximately 8 million acres of BLM-ad~is- <br />tered lands in the basin contain saline soils. Of this total, SLM has identified roughly., <br />180,000 acres of strongly saline soils, more than 1.5 million acres of moderately saline_ <br />soils, and TOughly 6.5 million acres wilh slightly saline soils. Refer to Appendix A for <br />salinity maps and an explanation of salinity classes. <br /> <br />Salt enters tributaries of the Colorado River from nonpoint sources such as surface runoff, <br />erosion, and ground water flows, and from point sources such as saline springs, spoil piles <br />at mines, and oil and gas production sites. <br /> <br />Salt concentrations on BU\.1lands are highest in marine shale geologic settings where <br />annual precipitation averages Jess than 12 inches. Most salt contributions from BL\1lands <br />to the Colorado River occur from nonpoint sources of salinity_ <br /> <br />It is extremely difficult to determine exact amounts of salt contributed from BLM lands. <br />Reasons for this difficulty are physical transport mechanisms associated with salt and <br />sediment movement, saline ground water flow, and variability in land ownership. <br /> <br />The physical transport mechanisms include surface runoff and sedimentation. Salts in <br />solution are readily transpoI1ed by overland flow. Salts associated with sediments are <br />transported by processes of erosion, sediment transpoI1. and disposition. Sediment and <br />salt yields refer to the amount of sediment and salt delivered from a watershed. Salinity <br /> <br />I <br /> <br />~ <br />. .,' <br /> <br /> <br />....'<0: <br />; '::.. ...~ 1 <br />".... ..'-'"...-- <br />~- ~'..:- -, <br /> <br />'. <br />....... <br />S <br />., <br /> <br />Strongly saline mancos shale rangeland in eastern Utah. <br /> <br />7 <br />