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~~~~J About 6,000 acres of cropland ,are not cultivated in anyone year. Irrigation water is obtained mostly from the. C,olorado River and is del ivered to the fields through Federai and pr'ivate canal systems involving more than 200 miles of canals and over 500 mi les of laterals. Q Q c.n ~ 3. Sal inity In The Grand Val ley The val ley contributes about 600,000 to 700,000 tons of salt annually to the Colorado River. It is assumed that most of these salts (gypsum, calcite and sodium sulphate) are leached from the soil and underlying Mancos shale and carried to the river by deep percolation through over i rr i gat i on and by seepage from water de I i very and tai Iwater col./ection ditches. Seepage losses from unl ined farm del ivery ditches, tai Iwater collection ditches and deep percolation from field irrigation are considered to be major sources of water that carries salt to the river. Salt loading is the major cause of sal inity increase in the Colorado River and has caused water qual ity problems for downstream water userS. 4. Climatic Conditions i~ ,:.:)\';:;> Climatic conditions vary in different parts of the Grand Valley and there is difference in temperature and precipitation between the east and west end of the valley. In general, the area has hot summers, mi Id winters, and a high percentage of sunny days. The hotte,st temperatures occur in July and August and could go ove~ 100 degrees for several days. The coldest temperatures occur in January and February and readings below zero are not unusual. The cl imatic summary for the Grand Junction area is presented in Appendix A. Average monthly temperatures and precipitation since ~he M&E program started are provided in this Appendix table. The average growing season varies from 154 days to 190 days in different parts of the Grand Valley. The Grand Va I I ey has an ar i d c I i mate and rece i ves between 8 to 10 inches of moisture annually depending on the area. In the last three to four years, extreme record low temperatures in February have been the norm. As a resu I t, the peach crop in the val ley has been destroyed in the last two years because of the cold freeze. Other fruit trees and grapes have also succumbed to the cold. In 1991, the temperatures were colder than normal (Apri I/May) in the spring and delayed crop planting (e.g. corn) and growth by about two weeks. Harvesting of corn was delayed by a few weeks because of cold and wet fall (refer to cl imatic summary in Appendix A). .:/,:,;:"l..> <,''liil -:~h? 3