Soil of the Month for May: Quinlan

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Red soil and red meat

Did you know that the Southern Great Plains produces 25% of the nation’s red meat? Get along little doggies and get ready to meet a red soil this month: Quinlan. (Disclaimer: Title is supposed be cute. Red soils don’t cause red meat).

The Quinlan series can be found in the Central Rolling Red Plains of south central Kansas, Oklahoma, and Texas (Figure 1). When you see this soil, “red dirt” will cross your mind (but please save the word “dirt” for soil out of place). The parent material for the soil is from sediments weathered from really old sandstone bedrock (250-298 million years old).


Figure 1. Soil series extent map for the Quinlan soil series showing its extent in Kansas, Oklahoma, and Texas. Map created using USDA-NRCS Official Soil Series Description website.


How do soils get their colors?

There are lots of reasons, but the driving forces are two of the five soil forming factors: weather (heat and water) and parent material (minerals). The hotter and wetter an environment is, the more that minerals weather and break down.  In the hottest, wettest places on earth (tropical rainforests), you will find the reddest soils. In south central Kansas, Oklahoma, and Texas, we have a lot of heat and some moisture, and that creates reddish-soils. Why? Because as minerals weather (break down), iron minerals such as goethite become the most prevalent and they weather very slowly. The Quinlan soil series has about 8 inches of topsoil, a few inches of red subsoil, and red sandstone bedrock at about 1 foot below the soil surface (Figure 2).

Figure 2. Quinlan soil monolith. Note the lack of soil horizon development, shallow profile depth, and reddish soil color. Photo by DeAnn Presley, K-State Research and Extension.

Not your typical Kansas soil

The topsoil in the Quinlan series is reddish brown, and that’s why it is not a mollisol. Back in our first Soil of the Month article (January/February), we explained that mollisols are formed from many, many years of prairie vegetation dying and enriching the soil in soil organic matter, giving mollisols their distinctive black color. The Quinlan soil does not contain very much soil organic matter. Remember our discussion earlier about heat coupled with some moisture causing Quinlan soils to be red? Hot temperatures and some moisture lead to rapid decomposition by microbes, and so soil organic matter (dark brown or black) doesn’t have much of a chance to accumulate.

So if it’s not a mollisol, how does the Quinlan classify? It’s an Inceptisol, which means that it is a pretty simple soil: Just an A horizon, a weak B (subsoil) horizon, and the C horizon which is soft sandstone. Inceptisol comes from the Latin word inceptum, which means beginning. Inceptisols are just beginning to show signs of profile development. You might think of these as “immature” soils.

There are over 1,500,000 acres of Quinlan soils mapped in the U.S., the majority of which are used for grazing but crops are sometimes grown on lesser slopes. Figure 3 is a photo of a Quinlan soil in Harper County, Kansas. Triticale for grazing was drilled into the previous year’s crop residues. Grazing cropland is an expanding practice, and many resources on this topic can be found at


Figure 3. Triticale no-tilled into crop residue on a Quinlan soil, grazed by cattle. Photo by DeAnn Presley, K-State Research and Extension.


For more information on soil color, see “The Color of Soil”, USDA-NRCS:

Here are links to the previous Soil of the Month articles for 2018:


The release of the May Soil of the Month article was delayed due to network issues associated with the Hale Library fire that occurred toward the end of May. Stay tuned in a couple of weeks for our June soil!





DeAnn Presley, Soil Management Specialist

Kathy Gehl, Soil Scientist and eUpdate Editor

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