STATE A.GRK ULTURAL SOCIETY. 277 



face is principally covered with decomposed granite. This great valley is 

 separated from the Bays of San Francisco and San Pablo by the Diablo 

 Range, which extends from the Straits of Carquinez in a southeasterly 

 direction about one hundred and fifty miles, where it terminates in low 

 ridges running out into the San Joaquin plain. This range has an average 

 elevation of about two thousand feet, an average width of about twenty 

 miles, and is poorly timbered; indeed, almost nude. 



Livermore Pass, in this range, has an elevation of six hundred and 

 eighty-six feet, and Pacheco Pass, one thousand four hundred and seventy 

 feet. " 



The trend of the valley, and all its walls, is southeasterly. 



Tills LONG VALLEY, Tins WALLED IN, 



Is veined by several considerable streams: the Sacramento, Pitt, Feather, 

 Yuba, American, Cosumnes, Mokelumne, Calaveras, San Joaquin, Kings, 

 White, and the Kern, all of which come out of the Sierra Nevada Moun- 

 tains. The two great rivers, the Sacramento and the San Joaquin, head' 

 in opposite directions, but approach and unite at Suisun Bay, through 

 which they empty into the Straits of Carquinez at San Pablo Bay. The 

 Coast Range mountains contribute but little water to this valley, save in 

 the Winter. The south end of the vallev contains two or three small lakes, 

 and several of the rivers are fringed by inconsiderable marshes. The 

 valley is nearly level throughout its length, and has an elevation of about 

 two hundred feet. This even surface is broken only by the Marysville 

 Buttes, which rise abruptly out of the plain. This is a range of volcanic 

 hills about six miles wide and twelve in length, with three peaks. The 

 valley is generally bare of native trees, though the oak grows to some 

 extent throughout. The substratum of the valley is a deposit of gravel 

 and sand, with a depth of about two thousand feet. The surface soil is 

 sand and dissolved volcanic material, mixed with vegetable mold. This 

 great underlying bed of sand and gravel is always thoroughly saturated 

 with water to within a few feet of the surface. The Winter rains saturate 

 the surface soil until the two moistures meet; but the Spring and Summer 

 evaporation dries the soil to an average depth of about two feet, leaving 

 the upper surface cracked, dry, and hard, drying every kind of vegetation 

 that does not extend its roots to the moisture below, or receive water from 

 irrigation. 



The soil at the south end of the valley is very largely composed of sand, 

 gravel, and hardpan, substances capable of absorbing and containing vast 

 accumulations of heat. 



We have now before us a general view of the topography of the valley 

 in which the northerly winds move. 



In studying the meteorology of this valley, we would naturally expect 

 the ratification of the valley atmosphere to draw in the cold air from the 

 Pacific Ocean, through the Golden Gate, the Diablo passes, and the Straits 

 of Carquinez. 



But the Diablo Eange, the narrowness of the Golden Gate and the Straits 

 of Carquinez, and the elevation of the Diablo passes, seem to prevent the 

 extensive and ready influx of ocean air, until certain contingencies occur, 

 which enable the ocean winds to overcome these obstacles. In the mean- 

 time, the only winds that visit the valley are the northwestern winds, of 

 which we are now writing. These northern winds are felt throughout the 

 valley, and to some extent in San Francisco, and in Napa Valley. As a 



