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Page 6 <br /> of 1:250, 000 and contour intervals of 50 feet. These maps were found to be <br /> of limited accuracy, particularly along streams and canyons. The lack of <br /> adequate vertical control considerably increased the difficulty of evaluating <br /> the geological and hydrological data available. Correlation of information <br /> from drillers' logs to determine contours of the base of the various forma- <br /> tions must be based on accurate surface elevations in order to determine <br /> the proper structural relationships. With variations in the estimation of <br /> the elevation of certain points ranging up to 50 - 100 feet, the task of trac- <br /> ing minor but significant changes in formation characteristics became quite <br /> formidable. A similar problem was encountered in developing maps of <br /> the level of water saturation in the aquifers. <br /> CLIMATE <br /> The climate of the study area can be characterized as semi- <br /> arid. It has low relative humidity, abundant sunshine, light rainfall, mod- <br /> erate to high winds and a large daily temperature range. The summers <br /> are hot and dry and the winters are normally mild. <br /> The average annual rainfall at Springfield is 14. 73 inches per <br /> year and is slightly more than 16 inches per year in the southeastern part <br /> of Baca County. It is interesting to note the changes that have occurred in <br /> the annual rainfall average in recent decades. The Springfield records <br /> date back some 58 years -- sufficient time to develop good data on precipi- <br /> tation. In 1930 the average annual precipitation at that location was 17. 33 <br /> inches based on 26 years of record. For the 22 year period from 1931 <br /> through 1952 the average declined to 15. 37 inches and during the 10 year <br /> period from 1951 through 1960 the average was only 13. 07 inches. The <br /> average for all the years of record is now 14. 73 inches, indicating that <br /> precipitation during recent decades has been significantly below normal. <br /> The cumulative deficit in rainfall from this 14. 73 inch average for the <br /> 15 year period ending in 1965 was around 17 inches and during that period <br /> reached a peak of over 26 inches. This shortage in rainfall increased the <br /> need for a supplemental supply from ground water sources. <br /> The average annual evaporation rate in the study area is in <br /> excess of 60 inches a year. Seventy percent of this total amount occurs <br /> during the summer period from May through October. <br />