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Type Location: Arapahoe County, Colorado. Approx- imately 1000 feet north and 100 feet east of the south- west comer of sec. 13, T 5 S, R 67 W. Range in Characteristics: These soils have mollic epipedons and argillic horizons. They have an abrupt textural boundary between the A and upper B2t hori- zons. Thin inconsistent A2 horizons may occur in some pedons. Thickness of the mollic epipedon may range from 7 to 19 inches, depth to calcareous material typi- cally ranges from 10 to 30 inches, thickness ofthe solum normally ranges from 40 to about 72 inche s and there should be no bedrock or strongly contrasting sub- stratums above 40 inches or immediately below the solum if thicker than 40 inches. Content of organic carbon normally ranges from .7 to 3 percent and de- creases uniformly with depth. Conductivity is typically less than 2 millimhos but should not exceed 16 millimhos where the soils are salt affected. Exchangeable sodium percentage is normally less than 3 percent but should not exceed 15 percent. The soils are 80 to 100 percent base saturated. Cation exchange capacity ranges from 70 to 90 milliequivalents per 100 grams of clay. These soils are developing in polylithologic types of parent materials and have a distinct textural discontinuity within their solums. The upper part of the solum has developed in silty materials presumed to be eolian in origin. The lower solum is developing in medium to moderately fine textured outwash materials from Den- ver and Arapahoe arkose formations containing a high proportion of medium and coarse angular granite sand. Mean annual soil temperature ranges from 470 F to 580 F and mean summer soil temperature ranges from 59" F to 79" F. Length oftime the soil temperature at 20 inches exceeds 41' F normally ranges from about 230 to 305 days. Length of time (cumulative) that the soil is moist in some part of the moisture control section while the soil temperature at 20 inches is above 410 F normally ranges from 56 to 152 days but in most years it should not be less than one-fourth or more than one-half of the time that the soil temperature is above 410 F. Color of the A horizon may range in hue from 5Y to 7.5YR, in value from 4 to 5 dry or 2 to 3 moist, and in chroma from 2 to 3. Reaction normally ranges from pH 6.1 to pH 7.8 (1:5 dilution unbuffered organic dye). Primary structure is usually granular or crumb but may be subangular blocky. Consistence ranges from soft to slightly hard. Color of the B2t horizon may range in hue from 5Y to 7.5YR, in value from 5 to 7 dry or 3 to 6 moist, and in chroma from 2 to 6. Reaction of the upper part normally ranges from pH 6.1 to pH 7.8 and that of the lower part from pH 7.8 to pH 8.6 (1:5 dilution unbuffered organic dye). Primary structure is usually prismatic but may be angular blocky. Texture is typically a silty clay in the upper part and a heavy clay loam to clay in the lower part but clay may range from 35 to 50 percent, silt from 20 to 50 percent, and sand from 5 to 40 percent with less than 15 percent fine or coarser sand in the upper part and more than 15 percent fine or coarser sand in the lower part, much of which is medium and coarse angu- lar granite sand. Oriented clay films occur in some part of this horizon. Visible calcium carbonate usually ac- cumulates in structural cracks in the lower part of the horizon although ped interiors are noncalcareous. Hue of the C horizon may range from 5Y to 7.5YR. Reaction normally ranges from pH 8.0 to pH 8.6 (1:5 dilution unbuffered organic dye). Calcium carbonate equivalent of the fine earth ranges from 4 to 14 percent. Texture is typically a loam or clay loam of less than 35 percent clay. COMPETING SERIES AND THEIR DIFFERENTIAE: These include the Dora, Onray, Platner, and Weld series. The Dora series differs in having a lithic contact above 40 inches or immediately below the solum if thicker than 40 inches. The Onray series differs in de- veloping in monolithic parent materials, in lacking a lithologic discontinuity within the solum, and in having finer textured C horizons with more than 35 percent clay. The Platner series differs in having developed in monolithic parent materials, in having thinner solums, in having higher proportions of sand in the upper part of the B2t horizon, and in having sandier C horizons. The Weld series differs in having developed in monolithic aeolean materials, in lacking a lithologic discontinuity with the solum, in having thinner solums, and in having siltier textured C horizons. 20