ISOTAKY. 13 



again called into vigorous action, and the country, which a few weeks before was a desert, is 

 now transformed into a flower garden. 



Vegetation. — The peculiar climate which I have described has given to the Sacramento a 

 vegetation very different from the district last considered. During the winter and spring the 

 ground is saturated with moisture, and is everywhere covered with a dense growth of herbaceous 

 plants. 



After the month of May, however, the process of evaporation succeeds that of deposition, 

 and by July the soil is dry and deeply cracked by the sun. The causes above enumerated have 

 doubtless been most efficient in giving the Sacramento valley its broad expanses of prairie, and 

 limiting the trees to a narrow belt bordering the streams ; these timber belts being also governed 

 as to their width and density by the magnitude of the streams which they follow, and the 

 quantity of moisture derived from them, absorbed by their roots from the earth, or by their 

 leaves from the air. Another feature of the climate of the Sacramento valley, common, also, 

 to all the interior of California and Oregon, has had its effect in determining the character of the 

 vegetation. From the fact, already mentioned, of the entire absence, during summer, of clouds 

 or mist, the sun's rays are not only permitted to fall with extreme power upon the surface 

 during the day, but the moment the heat ceases to be received from the sun it is radiated into 

 space with equal facility, and, as a consequence, the nights are always cool — the mercury falling 

 from above 100° to 15 o -70° Fahr. during the night. The result of all these influences is, that 

 the vegetation covering the greater part of the surface of the valley is not only annual in 

 character, but runs through all its changes during the winter and spring ; most of the plants 

 having formed, and many of them cast, their seed before the 1st of July. Hence many of the 

 wild and cultivated plants which occupy in their growth the whole of the tropical summer of 

 the eastern States would not flourish here. Of this class, the Indian corn may be regarded as 

 a typical example. We may here find the reason why its cultivation in California has been but 

 partially successful. 



LOCAL BOTANY. 



The immense area in central and southern California, including the greater part of the Sacra- 

 mento and San Joaquin valleys, as well as those portions of the coast mountains not occupied 

 by forest3, is covered with an almost uninterrupted growth of wild oat, (Avena/atua.) This 

 plant is regarded by our best botanists as an importation from the Old World, and yet very few 

 of those who see it as it grows in California can be made to believe that it was introduced by 

 the early Spanish settlers, and is only naturalized, not indigenous. It now covers surfaces of 

 rnau*y hundreds of miles in extent, both hill and plain, as completely as the grasses cover the 

 prairies of Illinois. In early summer the districts where this plant prevails have all the 

 appearance of being under high cultivation. The oat resembles very closely that cultivated at 

 home, and frequently stands as thick on the ground as the grain in our fields. The hills 

 and mountain sides bordering the bays of San Francisco and San Pablo are generally covered 

 with the wild oat, and are destitute of trees, except that here and there, in the ravines and on 

 the more broken surfaces, are a few grouped or scattered evergreen oaks, laurels, and buckeyes. 

 Of these, the oaks (Quercus agrifolia) are low and spreading, having much the appearance of 

 the apple trees in our orchards, and, combined with the wild oat, give to the country a civilized 

 and cultivated aspect. On the low lands, bordering the bays I have mentioned, a great variety 

 of flowering annuals find a place, and on the richer slopes of the hills dispute possession with 



