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WELD COUNTY, COLORADO, SOUTHERN PART 3-Aquolls and Aquents,.'`ravelly substratum. This nearly level map unit is on bottom lands and flood plains of all the major streams in the survey area. Aquolls, which have a dark colored surface layer, make up about 60 percent of the unit. Aquents, which have a lighter colored surface layer, make up about 35 percent. About 5 percent is Aquepts and Bankard sandy loam. These are deep, poorly drained soils that formed in recent alluvium. No one pedon is typical. Commonly the soils have a mottled, mildly alkaline to moderately al- kaline loamy or clayey surface layer and underlying material and are underlain by sand or sand and gravel within 48 inches. In places they have a gleyed layer in the underlying material. Most of the acreage is subject to flooding. The water table is at or near the surface early in spring and recedes to as deep as 48 inches late in fall in some years. ThesE~ soils are used for rangeland and wildlife habitat. Some small areas have been reclaimed by major drainage and leveling and are used for irrigated crops. The potential native vegetation is dominated by alkali sacaton, switchgrass, and western wheatgrass. Saltgrass, sedge, rush, and alkali bluegrass are also prominent. Potential production ranges from 3,000 pounds per acre in favorable years to 2,000 pounds in unfavorable years. As range condition deteriorates, the switchgrass, alkali sacaton, and western wheatgrass decrease and saltgrass, sedge, and rush increase. Management of vegetation should be based on taking half and leaving half of the total annual production. Seed- ing is difficult and costly because numerous tillage prac- tices :u•e required to eliminate the saltgrass sod. Switchgrass, western wheatgrass, alkali sacaton, tall wheatgrass, and tall fescue are suitable for seeding. They can be seeded into a clean, firm seedbed. Seedbed preparation usually requires more than 1 year to eliminate the saltgrass sod. A grass drill should be used. Seeding; early in spring has proven most successful. Wetland wildlife, especially waterfowl, utilize this unit. The wetland plants provide nesting and protective cover, as well as some food. The neazby irrigated cropland, where wildlife obtain much of their food and find protec- tive cover, makes this unit valuable to both wetland and openlar~d wildlife. Openland wildlife, especially pheasant, use this unit for cover and nesting. Deer fmd excellent cover in some areas. These valuable wildlife areas should be protected from fire and fenced to prevent encroachment and overuse by livesta~k. They should not be drained. These soils have good potential as a source of sand and sravel. Capability subclass VIw; Salt Meadow range site. 41-Nunn clay loam, 0 to 1 percent slopes. This is a deep, well drained soil on terraces and smooth plains at elevations of 4,550 to 5,150 feet. It formed in mixed allu- vium and eolian deposits. Included in mapping are small, long and nazrow areas of sand and gravel deposits and small areas of soils that are subject to occasional flooding. Some small leveled areas are also included. Typically the surface layer of this Nunn soil is grayish brown clay loam about 9 inches thick. The subsoil is light brownish gray clay loam about 14 inches thick. The upper part of the substratum is clay loam. The lower part to a depth of 60 inches is sandy loam. Permeability is moderately slow. Available water capacity is high. The effective rooting depth is 60 inches or more. Surface runoff is slow, and the erosion hazard is low. This soil is used almost entvely far irrigated crops. It is suited to all crops commonly grown in the area, includ- ing corn, sugar beets, beans, alfalfa, small grain, potatoes, and onions. An example of a suitable cropping system is 3 to 4 years of alfalfa followed by corn, corn for silage, sugar beets, small grain, or beans. Few conservation prac- tices are needed to maintain top yields. All methods of irrigation are suitable, but furrow ir- rigation is the most common. Barnyard manure and com- mercial fertilizer aze needed for top yields. Windbreaks and environmental plantings of trees and shrubs commonly grown in the area are generally well suited to this soil. Cultivation to control competing vegetation should be continued for as many years ae possible following planting. Trees that are best suited and have good survival are Rocky Mountain juniper, eastern redcedar, ponderosa pine, Siberian elm, Russian-olive, and hackberry. The shrubs best suited are skunkbush sumac, lilac, Siberian peashrub, and American plum. Wildlife is an important secondary use of this soil. The i cropland areas provide favorable habitat for ring-necked pheasant and mourning dove. Many nongame species can ~ be attracted by establishing areas for nesting and escape cover. For pheasants, undisturbed nesting cover is essen- tial and should be included in plans for habitat develop- ment, especially in areas of intensive agriculture. This soil has fair to poor potential for urban develop-~ ment. It has moderate to high shrink swell, low strength, and moderately slow permeability. These features create i problems in dwelling and road construction. Those areas that have loam or sandy loam in the lower part of the substratum are suitable for septic tank absorption fields and foundations. Some areas of this soil are adjacent to streams and are subject to occasional flooding. The poten- tial is fair for such recreational development as camp and picnic areas and playgrounds. Capability class I irrigated.