“Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past.”
—Charles Kellogg, The Soils That Support Us, 1956
“The soil is the great connector of our lives, the source and destination of all.”
—Wendell Berry, The Unsettling of America, 1977
“We must come to understand our past, our history, in terms of the soil and water and forests and grasses that have made it what it is.”
—William Vogt, Road to Survival, 1948
The General Nature of the Soils in Weld County
By NRCS Scientists: Will Owsley and Clark K. Harshbarger
Weld County soils are quite varied, from the sand hills in the south east portion to the exposed weathered bedrock buttes to the north (Soil Survey of Northern Weld County, 1970). This variation in soil type is due to the different types of parent materials that were deposited in Weld County thousands of years ago. Over time, Northern Colorado’s unique climate has left an erosional topography that supports grassland vegetation across much of Weld County. For this reason, cattlemen were the earliest permanent settlers, and remain a very significant part of Weld County’s landscape and economy. In an early expedition of the area, Major Stephen H. Long wrote, “In regard to this extensive section of country, I do not hesitate in giving the opinion that it is almost wholly unfit for cultivation, and of course, not inhabitable by a people depending upon agriculture for their subsistence.” But the early colonists established irrigation ditches to divert water from the Cache La Poudre River and the irrigation district quickly expanded as new diversions and ditches were constructed; many of which are still in operation today (See Land use Land Cover map). Today, Weld County ranks 9th in value of lands in agricultural production in the United States (USDA-NASS).
Much of Weld County is located in the northern portion of the Colorado Piedmont section of the Great Plains province. Weld County can be further divided into three distinct Major Land Resource Areas (MLRA); the Central High Plains Northern (67A), Central High Plains Southern (67B) and the Central High Plains Tableland (72). The General Soils Map clearly delineates landforms of dissected plains, valleys and sand hills that cover the landscape of Weld County (See STATSGO map). These landforms yield many different soil types that differ in inherent soil properties such as depth to bedrock, depth to seasonal high water table, ecological plant communities, soil texture, and clay mineralogy.
The largest portion of the county is on a gently undulating dissected plain. Areas of reworked old alluvium, wind-modified alluvium (sediments deposited by running water of streams and rivers) and loess (wind deposited silt size particles) make up the dominant parent materials across the dissected plain. This area holds the highest agricultural value due to access to irrigation, gently sloping landforms, and deep soil profiles. The Wiley-Colby-Weld map unit makes a large extent of the area under agricultural production in this portion of Weld County. The soils consist of deep, nearly level to gently sloping silt loam and loam surface textures. These soils formed from residuum (bedrock weathered in place) that is often capped by calcareous mixed alluvium. They are underlined by silty clay loam and clay textured subsoils.
A portion of the South Platte watershed drains all of central and southern Weld County. The South Platte River confluences with the Big Thompson River and again with Cache de la Poudre River, just outside of Greeley. Massive amounts of varying sizes of coarse sediment deposits in Weld County. The alluvium is a natural resource as a source and has been used for sand and gravel pits that have been instrumental in supporting the growth of the infrastructure across the region. All though quite different in size and appearance, all three rivers have their headwaters in the Front Range of the Rocky Mountains. Many of the larger sized gravels were deposited at the end of the last ice age when most of the Rocky Mountain glaciers melted, around 14,000 years before present. The Fluvaquents-Bankard-Alda map unit makes up a large extent of the area that is mapped on flood plains and flood plain steps in Weld County. These soils are very deep, poorly to excessively well drained, with stratified gravelly, sandy and loamy textured soils. The main use of this land is as riparian wildlife habitat and it provides a buffer to adjoining agriculture land from flooding and risk of erosion.
The most distinct geologic features in the county are the escarpments that extend across the northern portion of Weld County known as “Chalk Bluffs” and “Pawnee Buttes.” The bluffs consist of rock outcroppings of siltstone, commonly with a sandstone cap. Geologist believe that the sediment exposed in the buttes was deposited over 23 million years before present! Deposits from siltstone, sandstone and shale are found directly below the escarpments and the area is mainly used for cattle grazing and wildlife habitat. The Peetz-Bushman-Ascalon-Altvan map unit occurs in this portion of the county. The soils on and around the buttes are well drained, deep calcareous loams. The typical vegetation in this area is made up of a short grass prairie. Surface soil textures are sandy loam, loam in the uplands and clay loam in the drainage areas. Native grasses consist of blue gramma, buffalo grass, needle and thread and western wheat grass.
Conversely, in the southeastern portion of the county, the soils are dominated by eolian windblown sediments that have capped over the ancient terrace systems of the South Platte Valley. The Valent-Vona-Osgood soils in the south and south eastern part of the county consist of deep, nearly level to moderately sloping, well drained to excessively drained sands and sandy loams formed in eolian (eroded, deposited, or transported materials, primarily by wind) deposits. This is another area dominated by rangeland; although there are some small pockets of irrigated and dryland cropland limited by the sandy textures.
To learn more about the soils of Weld County visit the USDA-NRCS Web Soil Survey, http://websoilsurvey.sc.egov.usda.gov, where you can download data, link to historic published soil survey manuscripts and even create your own personalized soil map. As a side note, the initial soil survey area of Weld County was split into a northern and southern portion and are referred to as CO617 and CO618. There was also an unofficial soil survey completed of the Central Plains Experimental Range Station, which is around 16,000 acres of public land that is located around 5 miles north of Nunn, CO.