222 IRBIGATION INVESTIGATIONS IN CALIFORNIA. 



a clay loam. The narrow belt of dark-colored clay, or adobe land, extends from the neighborhood of 

 Merced City toward Stockton, where, northward of French Camp Slough and especially westward to 

 the Coast Range, really heavy adobe, or prairie soils, prevail very largely. To the southward of the 

 line of San Joaquin County adobe soils are found only in the river trough, and the soils of the west side 

 are prevalently sandy all the way to the Tejon Mountains. * * * 



The ancient deposits of the Kings River are represented by the "white ash" soils of the Central, 

 Washington, and other colonies; while those of the San Joaquin side are reddish, sandy loams, con- 

 trasting pointedly with the "white ash" lands. This distinction is said to be maintained to a greater 

 or le.ss extent nearly to the trough or edge of the "tule" belt to the westward; while to the eastward 

 of Fresno City both kinds of lancJs run out, as the foothills are approached, into a border belt of 

 brownish clay loam (here also called adobe). * * * 



The magnificent results of irrigation in the Fresno region, transforming what seemed an arid 

 waste into a maze of orchards, vineyards, and fields, showing the most luxuriant growth of a great 

 variety of products of the warm, temperate zone, can not readily be excelled as a cogent illustration of 

 the benefits of irrigation in all its phases. Owing to the porous nature of most of its soils, and the fact 

 that certain portions of the region are underlaid by more or less compact and impervi(ju8 calcareous 

 hardpan, it has also served conspicuously, in times past, to illustate the evils of overirrigation, resulting 

 in the temporary "swamping" of lower lying lands and the development of alkali where it was never 

 known before, and need not be hereafter under a rational system of drainage. 



In the lower lands of the country to the northward, to the Fresno plateau, on the San Joaquin 

 and Fresno rivers, as well as on Cottonwood Creek, we again find soils of a heavier grade, and with 

 large supplies of mineral plant food. 



BAINTAIiL. 



Stated roughly and in round numbers, the annual precipitation of rain and snow 

 on the high Sierras at the sources of San Joaquin River ha.s a mean of 50 inches. In 

 the lower mountains of its watershed the amount falls to 40 inches: on the foothills to 

 30; upon the higher plain to 20; and in the lowlaiid troiigh of the river, at and near its 

 great turn to the north, to 10 inches; from which localitj' it gradually increases in 

 amount as we proceed down the valley to the mouth of the river. 



FLOW OF THE KIVEK. 



The San Joaquin fluctuates widely in the course of the year, between a high or 

 flood water level and a low or autuuui flow. By gagings at Hamptonville (or Pol- 

 lasky) and also at Herndon, the maximum flow of the river has been recorded as 

 high as 59.800 cubic feet per second. The months of greatest flow are from January 

 to July, inclusive. On the other hand, its minimum flow has fallen as low as 150 

 feet at Herndon. The months from August to October include the period of low 

 water. In the winter and spring months the average discharge approximates to 

 5,000 to 6,000 cubic feet per second. 



CLIMATE. 



That part of the great interior valley drained by San Joaquin River contains 

 11,000 square miles. Its climate is quite different from that of the coast regions on 

 the west, as well as from that of the high Sierras on the east. The annual rainfall 

 is light, decreasing gradually from an average of about 12 inches in the lower valley 

 near Stockton, to about 5 inches in the upper part near Bakersfield, approximately 

 225 miles distant. 



Its atmosphere is very dry, particularly during the summer season; and con- 

 sequently very conducive to the evaporation of water, both from the streams and 

 the soil. The sunmier temperature is very high, but, owing to the dryness of the 



