The geological history of the valleys in Mesa, Delta and Montrose Counties is very similar. The following discussion of the development of the Grand Valley and its resulting soil characteristics thus applies to valley in Delta and Montrose County as well.

The Grand Valley is home to most of Mesa County's residents due to the fine growing conditions for plants and the `banana belt' environment we enjoy. While the climatic conditions are too temperate to raise bananas, this is the area where the majority of Colorado's tree fruits (peach, apricot, apple and pears) are produced and where Colorado's wine industry is being developed.

The Grand Valley itself was carved by the Colorado river (formerly called the Grand river) from soils laid down over eons by an inland sea we refer to as the Mancos sea. Geologists tell us that this sea advanced and retreated 29 times laying down layers of salty soil which over time developed into a formation we call Mancos Shale. By the time this sea totally withdrew from this area it left behind deposits as much as 4,150 feet thick. The resulting soils of the majority of the Grand Valley developed from these Mancos shale deposits. Later, volcanic flows capped parts of these deposits. Battlement Mesa east of this area in Garfield county and the Grand Mesa east of Grand Junction, Delta and Montrose were protected by these volcanic caps from the eroding effects of the rivers.

To the North and northeast of Grand Junction, the Mancos shale is capped by the Book Cliffs consisting of buff to yellowish-brown sandstone bedded with soft gray shale that has one or more beds of bituminous coal, and underlying, thick beds of sandstone that rest upon the marine Mancos shale. Today these cliffs rise about 3000 feet above the floor of the Grand Valley.

It seems inconceivable with today's 8 inches of annual precipitation received in the Grand Valley that this river could have eroded away so much area, but as much as 300 to 500 inches of precipitation may have fallen each year on the mountains and valleys of Western Colorado during the Pleistocene era (1.5 to 3.0 million years ago) when this erosion occurred. The melting of the continental ice sheets that covered the higher portions of the mountains in this area also contributed to this erosion.

Mancos shale breaks down into a very productive soil with a high water and plant nutrient holding capacity. When combined with our long growing season (up to 188 days), and a highly developed irrigation system, the Grand Valley can be an excellent area for growing plants. Gardeners should not, however, attempt to grow rhododendrons, azaleas, blueberry or other low pH requiring (acid-loving) plants due to the alkaline soil and the buffering affect of calcium carbonate found in these soils.

An inch of topsoil requires approximately 2,000 years to form in this area, therefore it is necessary to take special precautions to protect this important resource when excavating or leveling land. Contractors excavating basements should be encouraged to stockpile the existing topsoil and not cover it with the underlying non-decomposed salty Mancos shale.

As the Mancos deposits were laid down by the sea, salt was also deposited. These salts are mostly calcium sulfate (gypsum), a major component of wallboard and calcium carbonate, a major component of limestone. The solubility of calcium carbonate is very low so it is not a problem related to salinity, but does keep the soil alkaline in pH and makes it difficult to acidify soil

Plants have varying levels of tolerance to salt with low to very high levels of soil salts being common in this area. Salt levels of up to 139 mmhos/cm have been recorded for our soils, an impossible situation when attempting to grow plants. While it is not unusual to have 16 tons (32,000 pounds) of gypsum per acre slice of soil (an acre slice is considered to be an area of ground 6 inches deep for a total of 2,000,000 pounds), some area soils have up to 70 tons (140,000 pounds) of gypsum per acre slice. Newcomers as well as long term residents should always have a salt test run before making a final decision on purchasing a home site, orchard, vineyard or other site to be used for plant production. If you are making a decision from long distance, talk to your real estate agent or contact a consultant about having this test done. This is not meant to discourage newcomers to the area but to point out a concern that should be dealt with prior to the purchase.

The salts in these soils often can be leached out if drainage through the soil is improved with the addition of organic matter resulting in an excellent soil for plant growth. Cattle manures are higher in salts than most other animal manures and since many soils in the area already have high salt levels, adding cattle manure as an organic source can make the problem even more severe unless adequate water is applied to leach out these additional salts.

Well and spring water are commonly tested for bacteria and other pathogenic organisms prior to using it for domestic uses. When this water is to be used for watering plants, it should be checked for salt to avoid the chance of applying salty water to those plants.

The low rainfall enjoyed in this area is insufficient to take care of the needs of most plants. The Grand Valley receives approximately 8 inches of precipitation annually while many plants may require 36 inches or more of water per year. To the benefit of the Grand Valley, however is the abundance of irrigation water from the Grand Mesa as well as the Colorado river. As water is applied to crops, lawns and landscaped areas, salts in the soil are dissolved. As this water moves through shale aquifers, more salts are picked up by the water. Much of this salty water makes its way into the Colorado river, increasing the salt load of the river further down stream. This is the same salty water that is picked up by pumps inserted into wells drilled into the Mancos shale layers and appears as springs. When applied to most landscape plants as well as vegetables and flowers this water can cause the dehydration of roots and plant death.

The quality of the surface irrigation water available to the Grand Valley is quite good, with fairly low salt levels. As the season progresses and the run-off from the mountains become less, the salt levels in irrigation water understandably increases but typically remains below what would cause problems with our landscape plants and crops.

When the irrigation water runs off the end of a field or leaches through the soil, it is picked up by a series of drainage ditches that carry this waste water back to the river. This water is typically high in dissolved salts and if used to irrigate plants can cause their death. Prior to using water from a drain ditch the salt level of that water should be checked to determine its effect on plants.

In addition to saline soils, some areas of Western Colorado may be affected with sufficient quantities of sodium to impair plant growth and alter soil properties. The pH of these soils usually range between 8.5 and 10. The sodium destroys the tilth of the soil and leaves a layer of organic matter on the soil surface giving a dark color, hence the term `black alkali'. Because of the state of the soil it is difficult to till and relatively impermeable to water.

The pockets of sodium found in Mesa county are usually associated with gypsum. This combination should be considered advantageous as gypsum is necessary to free the sodium and reclaim these soils.

Gypsum should only be added to a Western Colorado soil if a sodium problem occurs and then only if sufficient gypsum is not already present to correct the problem. A soil test is required to determine the amount of sodium in a soil and the quantity of gypsum necessary to correct such sodic soils.

As with most soils in semi-arid regions, the organic level in these soils is typically less than 2% while an ideal soil is felt to contain 5% organic matter by volume. Adding and thoroughly working in 3 cubic yards of organic matter per 1000 square foot area is recommended each year for annual gardens. Six cubic yards of organic matter can be added per 1000 square foot area for perennial plants such as lawn areas, tree and shrub areas and perennial flower and vegetable gardens.

Soils in the Grand Valley of Mesa County, and the valleys of Delta and Montrose are seldom deficient of any plant nutrients other than nitrogen. The other two major soil plant nutrients (phosphorus and potassium) typically are high in concentration due to the parent soil material. It is not recommended that additional P or K be added unless a deficiency is determined by a soil test.

Applying phosphorus or potassium to a soil when excessive amounts already exist, can result in nutrient imbalances that adversely affect plant growth. Research show that excessive amounts of phosphorus can increase iron deficiency in monocots (i.e. grasses).

The higher communities of Mesa, Delta and Montrose county have soils formed from sandstone sediments deposited from surrounding formations over top of the shale. The valley soils that butt up against the Grand Mesa also have developed from these sandstone sediments. Even in these areas, however, the Mancos shale controls many of the characteristics of these soils as evidenced by pockets of salty soils in these areas. While these higher areas are less impacted with salts, the growing season is considerably shorter than in the valley negating any advantage offered to plants by the lower salt level soils.

The more sandy soils on the Redlands area due west of Grand Junction are a result of the Uncompahgre uplift. This uplift, after ages of severe geologic erosion has caused the exposure of geological formations that were initially situated far below the 4000 foot thick layer of Mancos shale. The Uncompahgre uplift extends for some 100 miles from the San Juan Mountains to the south into eastern Utah. While the growing season in the Redlands area is not as long as occurs in the Palisade area to the east of Grand Junction, this area still has a relatively long growing season (179 days).

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