These geographical conditions have had important consequences climatically and economically and especially historically. The altitude and irregularity of the land have produced widely separated extremes of temperature, although as a general rule a happy medium is maintained. To geographical causes, also, are due the alternating seasons of rain and drought in most of Spain, especially in Castile, Valencia, and Andalusia, which have to contend, too, with the disadvantages of a smaller annual rainfall than is the lot of most other parts of Europe and with the torrential rains which break the season of drought. When it rains, the water descends in such quantity and with such rapidity from the mountains to the sea that the river beds are often unable to contain it, and dangerous floods result. Furthermore, the sharpness of the slope makes it difficult to utilize these rivers for irrigation or navigation, so swift is the current, and so rapidly do the rivers spend themselves. Finally, the rain is not evenly distributed, and some regions, especially the high plateau country of Castile and La Mancha, are particularly dry and are difficult of cultivation. [Sidenote: Beneficial effects.] On the other hand the geographical conditions of the peninsula have produced distinct benefits to counterbalance the disadvantages. The coastal plains are often very fertile. Especially is this true of the east and south, where the vine and the olive, oranges, rice, and other fruits and vegetables are among the best in the world. The northern coast is of slight value agriculturally, but, thanks to a rainfall which is constant and greater than necessary, is rich pastorally. Here, too, there is a very agreeable climate, due in large measure to a favoring ocean current, which has also been influential in producing the forests in a part of Galicia. These factors have made the northern coast a favorite summer resort for Spaniards and, indeed, for many other Europeans. The mountains in all parts of the peninsula have proved to contain a mineral wealth which many centuries of mining have been unable to exhaust. Some gold and more silver have been found, but metals of use industrially--such, for example, as copper--have been the most abundant. The very difficulties which Spaniards have had to overcome helped to develop virile traits which have made their civilization of more force in the world than might have been expected from a country of such scant wealth and population.[3] [Sidenote: Geographical isolation the cause of Spanish individuality.]