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• Page 6 • <br />This unit is composed of two major components. About 45 percent of the <br />unit is rock outcrop, mainly sandstone, with some small outcrops of shale. <br />Another 49 percent of the unit has shallow soils, less than 20 inches, <br />over underlying sandstone acid some shale. These soils are stony and <br />usually have loamy, light-covered suiface layers. The remaining 6 per- <br />cent of the unit is made up of soils with dark=colored surface layers and <br />mixed alluvial soils in the Dolores and San Miguel River bottoms. <br />s , ~ <br />' _ <br />1 <br />Soil Mapping .Unit 4: Ioderately dark-colored deep soils of the mesas and <br />valleys 1 <br />i 7 <br />t <br />This mapping unit occupies several scattered arc as from Gateway to <br />?+ozKood above the Dolores sand San Miguel Rivers. ?'ost of the 'other <br />delineations a;:e along the south and west boundaries of the basin. This ' <br />unit. is of moderate extent and encompasses about 10 percent of the basin. ' <br />The landscape is charar_terized by large, nearly level to ye;~tly sloping, <br />upland valleys, and gently sloping r,',esas. Individual mesas are separated <br />by nw~erous drairagr-Y;ays that are entrr_nr_hrd to depths of 100 to 500 feet <br />and have step sandstone walls. The dominant cover is scgeorush with <br />some pinyon-juniper and rabbit~irush. 1!ost the irrigated and dry crop <br />land~and potentially irrigable land of she basin is within this unit. . <br />i <br />t•;ost of •the soils in this unit are forged in rEddish-brown eolian <br />materials. Otheis are residual or al.luvi_al frcm sandstone and shale. <br />P.bout Q5 :a rcent of the un.i.t is well-drain.ad, deep and mcderat r_ly dcap, ' <br />with dark-colored surface Payers. These soils are noncalcareous to <br />depths of 10 to 24 inches but have slight to moderate zones of lime <br />accw~ulation. They are moderately r_oarse to moderately fine textured <br />with su];soi.ls that are usually finer textured than the surface layers. <br />Another 40 percent of tiie unit is similar to the above except the surface <br />layers are rr~ederately dark-colored and have a lcwer organic matter con- <br />tent. Depth to calcareous material is 6 to 12 inches. Subsoil textures __ <br />range frcm moderately coarse to fine. Lime-cemented cobble and gravel _ <br />are ce.;mon below the subsoil. about 10 percent of the unit is less than <br />20 inches deep over sandstone and shale. The remaining 5 percent consists <br />of alluvial soils in the drainageways. <br />Soil t•'_~i~~ Unit 5: Dark _colored soils of the cold ; ~ovntain ~slores <br />There are several delineations of this unit in both Colorado and Utah. <br />It is one of the -~ost~excensive units, comprising about 22 percent of the <br />L-a sin, although precipitation is plentiful, the short gre•.ui.ng season <br />]'nits crop produMion to mainly I:ay and pasture, <br />7 <br /> <br /> <br />