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GRANDE COUNTY AREA, COLORADO
<br />in the mirlrlle 80's and a minimum in the low 40's. The
<br />highest. temperature recorded at Del Norte was O1° F,
<br />and the lowest -2G". The average summer tempera lure
<br />is about 6'L'', and the average annual temperature is
<br />about 43". At &fonte Vista the highest temperature
<br />recorded +vas 94°, and the lo+vest - ;7°. The average
<br />summer temperature is about 61°, and the average
<br />annual tempernhn'e 41°.
<br />The length of the growing season varies considerably
<br />from year to cexr. It also caries between Dlonte Vista,
<br />in the central part of the major irrigated area, and
<br />De] Norte, on the edge of the foothills. Table 12 shotas
<br />probabilities of last freezing temperature in spring and
<br />first in fall at Del Norte. The average length of the
<br />groteing season is about 95 clays at Monte Vista and
<br />about I ] 0 days at Del Nm'te. This season is long enough
<br />for two cuttings of alfalfa, and it is generally sufficient
<br />time fur potatoes, barley, oats, peas, lettuce, cauliflower,
<br />and cabbage. The last 32° or lover temperature in
<br />spring is generally between May 25 and June 15 at
<br />Del Norte and bet++'een June 2 and June 18 at Monte
<br />Vista. The first 32° or lower temperature in the fall is
<br />generally between September 9 and October 3 at Del
<br />Norte and between September 2 and Sptember 22
<br />at Monte Vista.
<br />Frost can occur in evely month. It penetrates to a
<br />depth of ? to 3 feet every year. The soil is generally
<br />frozen from mid-November to mid-March, but thaws
<br />by April.
<br />Strong winds occur in spring and early in summer,
<br />causing much blo+cing dust before crops start to grow.
<br />Winds are mostly from the southwest. The wind does
<br />not normally blow strongly during fall and winter,
<br />unless it precedes a storm front. Spring and summer
<br />winds do the most damage by drying out the soil and
<br />making more frequent irrigation necessary.
<br />Snowfall averages about 35 inches per year in the
<br />valley, but is more in the mountains. It is generally
<br />light between November and April. During winter,
<br />sno+v normally stays on the ground for several weeks
<br />at a time.
<br />Farming
<br />The Rio Grande County Area is mainly an agricul-
<br />tural community. The principal industry is irrigated
<br />farming and cattle and sheep raising. There are at
<br />present about 488 operating farms and ranches in the
<br />Area. 114ost farms are 100 to 320 acres in size. Most
<br />ranches are more than 690 acres.
<br />The main crops and the approximate acreage are
<br />alfalfa and irrigated pasture, 31,000 acres; potatoes,
<br />23,000 acres; barley, 30,000 acres; oats, 6,000 acres; and
<br />meadow hay, 20,000 acres. Other crops, such as lettuce,
<br />cabbage, cauliflower, peas, and spring ++•heat, grown to
<br />a lesser extent, amount to about a total of b,000 acres.
<br />Ranchers raise cattle and sheep, and many do some
<br />irrigated farming. M;my farmers also have livestock-
<br />cattle, sheep, and hogs. The number of livestock on
<br />farms and I.vtches varies from year to year. Cattle
<br />generally number 13,000 to 28,000; sheep 55,000 to
<br />100.00(1; and hogs :1,000 to ]0,000.
<br />87
<br />Literature Cited
<br />(1) American Association nC State Highway [and Transporta-
<br />tion] OOicmis. 19G1. Sta nda rrl specifications for highway
<br />materials and methods o[ sampling and testing. E. 8, °_ v.,
<br />illus.
<br />(2) American Sucicty of Testing and Materials. 1974. Method
<br />for classification of soils for engineering purposes. ASTM
<br />Stand. D '1487-fig. h+ 1974 Annual Rook of ASTM Stand-
<br />ards, Part 19, 4fi4 pp., illus.
<br />(3) Franklin, W. T.; Whitney, Robert S., Code, W. E.; and
<br />Reece. R. C. 1957. Reclamation and management of saline-
<br />sodium soils, Mosca-Hooper area, San Luis Valley; Colo-
<br />rado Agricultural Experiment Station, general series
<br />paper 6G7, 2R pp.
<br />(4) Harrington, H. P. 1954. Manual of the plants of Colorado.
<br />GGG pp., Denver.
<br />(5) Hitchcock, A. S. 1950. Manual o[ grasses of the United
<br />States. U.S. Dep. Agric. Misc. Pub. 200, 1,951 pP., illus.
<br />(G) Larsen, F.. 5. Jr., and Cross, W. 195G. Geology and petrol-
<br />ogy of the San Juan region, southwestern Colorado. Geol.
<br />swv. prof. paper 258, 303 pp.
<br />(7) Powell, W. J. 1953. Ground-water resources oC the San
<br />Luis Valley, Colorado: U.S. Geol. Surv. Water-Supply
<br />Paper 1.319, 289 pp.
<br />(8) Portland Cement Association. 19G°. PCA soil primer. 8G
<br />PP~~ illus.
<br />(9) Richards, L. A., Ed. 1954. Diagnosis and improvement of
<br />saline and alkaline soils. U.S. Dep. of Agric. Handb. 60,
<br />1G0 pp., illus.
<br />(10) Soil Sw~vey Staff. 1960. Soil classification, a comprehen-
<br />sive system, 7th approximation. U.S. Dep. Agric, 265 pp.,
<br />illus. [Supplements issued in March 1961 and September
<br />1968.]
<br />(11) Steven, T. A., and Ratte, J. C. 1960. Geology and ore
<br />deposits of the Summitville district, San Juan Mountains,
<br />Colorado. U.S. Geol. Surv. Prof. Paper 343, 70 pp.
<br />(12) United States Department oC Agriculture. 1951. Soil swvey
<br />manual. U.S. Dep. Agric Handb. 18, 503 pp., illus.
<br />(13) .1955. 1Vater. U.S. Dep. Agric. Agric 1'bk 120,
<br />illus.
<br />(14) United States Department of Interior. 1935. Geologic map
<br />of Colorado. Geol. Sui1~. in coop. +vith Colo. State Ceol.
<br />Sure. Brl and Culo. Metal and Mining Fund, 2 map sheets.
<br />(15) Upson, J. E. 1939. Pltysiographic subdivisions of the San
<br />Luis Vallee, Southern Colorado. Jour. of Geol., 47, No. 7,
<br />PP. 721-736.
<br />Glossary
<br />Aggregate, soil. Many fine particles held in a single mass or
<br />cluster. Natm~al sail aggregates, such as crumbs, blocks, or
<br />prisms, are called peds. Clods are aggregates Produced by
<br />tillage or logging.
<br />Alkali soil. Generally, highly alkaline soil. Specifically, an alkali
<br />soil has so high a degree of alkalinity (pH 8.5 or higher)
<br />or so high a percentage of exchangeable sodium (15 percent
<br />or more of the total exchangeable bases), or both, that
<br />the growth of most crop plants is low from this cause.
<br />Alluvium. Soil materials, such as sand, silt, or clay, that has
<br />been deposited mi land by streams.
<br />Available water rapacity (also termed available moisture capa-
<br />city). The capacity of soils to hold water available for use
<br />by most plants. IC is commonly defined as the difference
<br />behveen the amount of soil water at field capacity and the
<br />amount at wilting point. [t is commonly expressed as inches
<br />of water per inch of soil.
<br />Calcareous soil. A soil containing enough calcium carbonate
<br />(often with magnesium carbonate) to effervesce (fizz)
<br />visibly when treated with cold, dilute hydrochloric acid.
<br />Clay. As a soil separate, the mineral soil particles less than
<br />0.002 millimeter in diameter. As a soil textural class, soil
<br />material that is 40 percent or more clay, less than 95 per-
<br />centsand, and less than 40 percent silt.
<br />Clay film. A thin coating of clay on the surface of a soil aggre-
<br />gate. Synmiyms: clay coat, clay skin.
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