|
DELTA-MONTROSE AREA, COLORADO 47
<br /> Climate water has been in short supply through a governing
<br /> The climate of most of the Delta-Montrose Area is period in the genetic history of the soils, it would be
<br /> arid-continental. Summers are hot and dry, and winters expected that, in relatively permeable parent material,
<br /> cold and dry. The average annual precipitation at the the depth to which readily soluble calcium compounds
<br /> Delta Weather Station, in the north-central part of the have been transported would be comparatively shallow,
<br /> survey Area, is 8.3 inches. Nearly 6 inches of that total that the soils and the individual horizons would be thin,
<br /> falls during the months from April to October. Only and that removal of soluble calcium compounds from
<br /> in the months of July and August is the average rain- the upper soil horizons would not have been complete.
<br /> fall more than 1 inch. The average annual temperature The morphology of the soils of most of this Area is
<br /> is 510 F., and the average temperature for the months in accordance with these assumptions. Virgin soils that
<br /> of June, July, and August is 72°. The average frost- have distinct horizons have a solum less than 20 inches
<br /> free season is 146 days. thick, have a strong accumulation of secondary calcium
<br /> At the Montrose Weather Station, in the south-central carbonate at a depth of 12 to 16 inches, and have been
<br /> part of the survey Area, the average annual precipita- leached sufficiently to be noneffervescent or acid in only
<br /> tion is 9.1 inches. Of this total, 6.1 inches falls during the uppermost few inelies. It seems probable, that the
<br /> the summer months of April through October. In the amount and distribution of precipitation have been about
<br /> months of April, August, and September, the average the same as at present through a large part of the genetic
<br /> rainfall is 1 inch or more. The average annual tempera- history of the soils. If the present conditions represent
<br /> ture is 48.5°, and the average temperature for the months only a stage of cyclic variation, then the total genetic
<br /> of June, July, and August is 691. The average frost- effect of such variation has been the same as though
<br /> free season is 152 days. the supply of moisture had been short throughout the
<br /> Data recorded at these two weather stations charac- period of soil genesis.
<br /> terize the climate of most of the survey Area but are The soils in Bostwick Park and in the southeastern part
<br /> not representative of the climate in Bostwick Park and of the Area show evidence that, for at least a controlling
<br /> the southeastern parts of the Area. No precise weather period in their genetic history, they received greater
<br /> data for these sections are available,but the general char- amounts of precipitation than the soils in the rest of
<br /> acter of the climate can be approximated by projecting the Area. In these localities, virgin soils that have
<br /> data from stations in similar areas. distinct horizons have a soluim more than 24 inches thick,
<br /> Most of the Delta-Montrose Area is at elevations of have a less strongly developed ca horizon, are leached
<br /> 5,000 to 6,500 feet. Elevations in Bostwick Park and in of free carbonate to a depth of 10 to 20 inches, and
<br /> the southeastern part of the survey Area range from have a thicker and darker-colored surface horizon. A
<br /> 7,000 to 5,000 feet. It is to be expected that mean tem- difference in vegetation is further evidence that pre-
<br /> peratures will be lower at these higher elevations, and cipitation was more abundant. In these higher localities,
<br /> that the average precipitation.will be greater. By pro- the vegetation consists of brush and scattered trees, but
<br /> jecting data from the Norwood Weather Station, which in the rest of the Area the vegetation consists of grass
<br /> is at an elevation of 7,017 feet and about 35 miles south- and sage.
<br /> west of Montrose, it is to be expected that the average Although the pattern of precipitation may have dif
<br /> annual precipitation will be about 16 inches, that pre- fered from the present pattern at times during the soils
<br /> cipitation will exceed 1 inch in all but 3 months of each genetic history, the general relationship between present-
<br /> year, and that the mean annual temperature will be day variations in precipitation within the survey Area
<br /> approximately 45°. In June, July, and August, the are reflected in differences in soil morphology. Moreover,
<br /> temperature will average about 64°. soil morphology in the various parts of the Area is
<br /> The effect of the climate on soil development can only consistent with what could logically be anticipated had
<br /> be approximated, since recorded weather data cover only the present-day precipitation pattern been consistent
<br /> a period of 30 to 50 years, whereas the time required throughout the soils' genetic history.
<br /> for development of distinct soil horizons in this Area The relationship between temperature and soil mor-
<br /> may be measured in thousands of years. It would be phology in the Delta-Montrose Area is more obscure
<br /> unsound to assume that the recorded data represent a than that between precipitation and soil morphology.
<br /> true picture of the climate over all or even a major This obscurity is due partly to the lack of sib iificant
<br /> portion of the genetic history of the soils. It is possible, variations in temperature within the survey Area and
<br /> however, to draw logical parallels between general char- partly to the fact that in this Area temperature influ-
<br /> acteristics of the climate and general characteristics of ences soil genesis mainly through determining the effec-
<br /> the soils. Such an approach to the ,genetic impact of tiveness of moisture. Thus, the effect of temperature is
<br /> climate is of considerable value in the understanding of so interwoven with the effect of precipitation that it is
<br /> soil genesis, even though it is recognized that the climatic impossible to separate them precisely.
<br /> history of the soils cannot be reconstructed precisely. The hot summer temperatures that coincide with
<br /> The amount of water available and the distribution periods of maximum precipitation in this Area materially
<br /> of water in relation to temperature are of prime im- decrease the effectiveness of the moisture. Evapora-
<br /> portance in soil genesis. They play a major role in tion is very rapid in most of the Delta-Montrose Area
<br /> the growth and activity of organic life in and on the during the hot summer months, and much of the rainfall
<br /> soil, in the physical translocation of substances in solu- during this period evaporates before it has any effect on
<br /> tion or suspension, and in controlling the rate and di- soil genesis. The result is the same as that of a reduction
<br /> rection of chemical processes. If it is assumed that in the total amount of precipitation.
<br /> �ofzl
<br />
|