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<br />- ,._ ,,". .0>' <br />" ~ <br />.:'Ju-~ ,) <br /> <br />. <br /> <br />CHAPTER III <br /> <br />PROJECT LAlVDS--BASALT -PROJECT <br /> <br />Soils <br /> <br />SoilS of the project area have developed under the controlling influ- <br />ence of a semiarid climate. They are relatively low in organic matter <br />compared with soils developed in warmer and more humid climates but are <br />sufficiently fertile to produce good crop yields under adequate irriga- <br />tion. Moat of the soils are alluvial and have been derived principally <br />from the formations surrounding the project areas. Basaltic boulders <br />and cobbles are found in small amounts in the soil mantle over much of <br />the project area. <br /> <br />. <br /> <br />The s.oil textures range from loams to light clays. The most preva- <br />lent soil is a good friable clay loam usually in excess of 5 feet in <br />depth. Soil colors range from black to reddish brown topsoils to pale <br />brown subsoils. The permeability is generally very good. The natural <br />vegetative. cover consists of scrub oak and sage at the higher elevations <br />and heavy grmrth of sagebrush and grass at the lower elevations. Pinon <br />and juniper are found on the broken lands and escarpments surrounding the <br />benches. <br /> <br />Drainage <br /> <br />The project lands have generally good natural drainage characteris- <br />tics. Most of the lands have moderately steep slopes. deep soils under- <br />lain with basaltic rocks, and generally have access to deep natural <br />drainage outlets. Presently developed lands have been irrigated over an <br />extensive period without developing major drainage deficiencies. <br /> <br />Exposed soil profiles show the soils in most places to be adequately <br />deep to an impervious barrier which is generally bedrock. The water <br />moves down through the permeable soil mantle until it comes in contact <br />with the impervious barrier. It then mOVes out into a natural drainage <br />channel which removes the ,;ater from the area. <br /> <br />SeGpage and runoff from higher areas now drain into the saucer-like <br />Spring Valley. resulting in a high ,vater table. '['his condition could be <br />alleviated by the construction of drains. <br /> <br />. <br /> <br />Drainage deficiencies may develop with the increased water supply <br />provided by.the project so that some project drainage costs are included <br />in project cost estimates. <br /> <br />18 <br /> <br />