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2 <br />oats, 5,000 acres; and potatoes, 5,000 acres. Lettuce is <br />grown on about 500 to 1,000 acres in most years. <br />Climate <br />Summers are warm or hot in most valleys and much <br />cooler in the mountains. Winters are cold in the moun- <br />tains. Valleys are colder than the lower slopes of adja- <br />cent mountains because of cold air drainage. Precipita, <br />tion occurs in the mountains throughout the year, and a <br />deep snowpack accumulates during winter. Snowmelt <br />usually supplies much more water than can be used for <br />agriculture in the county. In valleys, precipitation in <br />summer falls as showers; some thunderstorms occur. In <br />winter the ground is covered with snow much of the <br />time. Chinook winds, which blow downslope and are <br />warm and dry, often melt and evaporate the snow. <br />Table 1 gives data on temperature and precipitation <br />for the survey area, as recorded at Manassa for the <br />period 1952 to 1974. Table 2 shows probable dates of <br />the first freeze in fall and the last freeze in spring. Table <br />3 provides data on length of the growing season. <br />In winter the average temperature is 21.6 degrees F, <br />and the average daily minimum temperature is 4 de- <br />grees. The lowest temperature on record, which oc- <br />curred on January 12, 1963, is -34 degrees. In :summer <br />the average temperature is 61.4 degrees, and the aver- <br />age daily maximum temperature is 79.6 degrees. The <br />highest recorded temperature, which occurred on July <br />13, 1971, is 94 degrees. <br />Growing degree days, shown in table 1, are equivalent <br />to "heat units." During the month, growing degree days <br />accumulate by the amount that the average temperature <br />each day exceeds a base temperature (40 degrees F). <br />The normal monthly accumulation is used to schedule <br />single or successive plantings of a crop between the last <br />freeze in spring and the first freeze in fall. <br />Of the total annual precipitation, 5.52 inches, or 71 <br />percent, usually falls in April through September, which <br />includes the growing season for most crops. In 2 years <br />out of 10, the rainfall in April through September is less <br />than 3.95 inches. The heaviest 1-day rainfall during the <br />period of record was 1.45 inches on August 5, 1954. <br />There are about 44 thunderstorms each year, 30 of <br />which occur in summer. <br />Average seasonal snowfall is 28 inches. The greatest <br />snow depth at any one time during the period of record <br />was 11 inches. On the average, 4 days have at least 1 <br />inch of snow on the ground, but the number of such <br />days varies greatly from year to year. <br />The average relative humidity in midafternoon in spring <br />is less than 35 percent; during the rest of the year it is <br />about 45 percent. Humidity is higher at night, and the <br />average at dawn is about 77 percent. The percentage of <br />possible sunshine is 77 in summer and 73 in winter. The <br />prevailing wind is from the south-southeast. Average <br />windspeed is highest, 10.4 miles per hour, in April. <br />SOIL SURVEY <br />Climatic data in this section were specially prepared <br />for the Soil Conservation Service by the National Climat- <br />ic Center, Asheville, North Carolina. <br />How this survey was made <br />Soil scientists made this survey to learn what kinds of <br />soil are in the survey area, where they are, and how they <br />can be used. The soil scientists went into the area know- <br />ing they likely would locate many soils they already knew <br />something about and perhaps identify some they had <br />never seen before. They observed the steepness, length, <br />and shape of slopes; the size of streams and the general <br />pattern of drainage; the kinds of native plants or crops; <br />the kinds of rock; and many facts about the soils. They <br />dug many holes to expose soil profiles. A profile is the <br />sequence of natural layers, or horizons, in a soil; it ex- <br />tends from the surface down into the parent material, <br />which has been changed very little by leaching or by the <br />action of plant roots. <br />The soil scientists recorded the characteristics of the <br />profiles they studied, and they compared those profiles <br />with others in counties nearby and in places more dis- <br />tant. Thus, through correlation, they classified and <br />named the soils according to nationwide, uniform proce- <br />dures (14). <br />After a guide for classifying and naming the soils was <br />worked out, the soil scientists drew the boundaries of the <br />individual soils on aerial photographs. These photo- <br />graphs show woodlands, buildings, field borders, roads, <br />and other details that help in drawing boundaries accu- <br />rately. The soil map at the back of this publication was <br />prepared from aerial photographs. <br />The areas shown on a soil map are called soil map <br />units. Some map units are made up of one kind of soil, <br />others are made up of two or more kinds of soil, and a <br />few have little or no soil material at all. Map units are <br />discussed in the sections "General soil map for broad <br />land use planning" and "Soil maps for detailed plan- <br />ning." <br />While a soil survey is in progress, samples of soils are <br />taken as needed for laboratory measurements and for <br />engineering tests. The soils are field tested, and interpre- <br />tations of their behavior are modified as necessary <br />during the course of the survey. New interpretations are <br />added to meet local needs, mainly through field observa- <br />tions of different kinds of soil in different uses under <br />different levels of management. Also, data are assem- <br />bled from other sources, such as test results, records, <br />field experience, and information available from State <br />and local specialists. For example, data on crop yields <br />under defined practices are assembled from farm rec- <br />ords and from field or plot experiments on the same <br />kinds of soil. <br />But only part of a soil survey is done when the soils <br />have been named, described, interpreted, and delineated <br />on aerial photographs and when the laboratory data and