Most of the water supply for crops comes from the mountains of the State.  Falling as rain or snow during the winter, it is held in reservoirs and as snowpack until needed during the growing season.  A smaller part of the State’s water requirement is met by the importation of water from the Rockies via the Colorado River.  This water is used in the southeastern Desert and the south coastal area.  Within the State more than 70 percent of the streamflow is generated in the area north of the latitude of Sacramento, while about 80 percent of the water requirements lie south of this line.  Thus, distribution of water is a major concern within the State.

The long growing season characteristic of most of the valley areas where agriculture is concentrated is an important factor in the production picture.  Some parts of the State are able to produce off-season truck crops and vegetables.  Today’s transportation networks carry these crops to all parts of the country and overseas.  Some crops are grown that require a long freeze-free season.  Others require the very high temperatures found only in some parts of the desert.  The long dry spell of the summer period facilitates the planting, cultivation, and harvest of many crops, and isolated late spring, summer, or early fall rains can possibly cause more damage than good.  Drying winds occasionally cause damage to developing crops.  Splitting of ripening fruit sometimes results from unseasonable showers at an inappropriate time.  In general, however, the distrubution of temperature and precipitation is highly favorable for most agricultural enterprises.