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36 dillera is crossed near the snow line, en route to Yungas, at an altitude of about 15,000 feet on the northwest side of Illimani, and en route to Sorata, Mapiri, and Tipuani at an altitude of about 17,000 feet on the northwest side of Illampu, while the snow line of the intervening chain, which forms a lofty serrated ridge, is approximately 15,000 feet.

La Paz, the metropolis and commercial center of the Republic, situated in the Quebrada del Choqueyapu, 650 feet below Lake Titicaca, and about 12,250 feet above the sea, in latitude and longitude  has a mean annual temperature of about  as correctly stated by Dr.  Weddell, a traveling naturalist of the Museum of Natural History of Paris in his "Travels in the North of Bolivia," published in Paris in 1853.

The following translation from the above work, taken from the Report of the Statistician of the Department of Agriculture (No. 89, New Series, 1891, p. 553), will be of interest in this connection:

The climate of La Paz is such as the Bolivians call cabezeras de valle (head of the valley). Its mean annual temperature is about 10° C. (50° F.), or somewhat less than that of Paris, generally reckoned at 10.8° C. (51.4° F.). The annual range of temperature at La Paz, however, is very different from that at Paris, being less hot in summer and less cold in winter. The result of a long series of observations made in this part of Bolivia, and [sic]commuicated to me show the extremes of temperature to be from -7° C. (+19.4° F.) to 23° C. (73.4° F.).

In 1850 the lowest temperature observed in June, there the coldest of the year, was only -4.44° C. (24° F.), while at Paris hardly a winter passes when the thermometer does not fall below -10° C. (14° F.). It might be concluded from these data that the temperature of La Paz is quite uniform, and such, indeed, would be the case did not the usual clearness of the sky render loss of heat by radiation very considerable, so that the nights are generally much colder than the day, while, in consequence, pulmonary diseases are quite prevalent there. Though the thermometer frequently falls below the freezing point at La Paz, plants are rarely frozen. This is because at this great height the air is very dry. I was led to notice this by the fact that the Indians, when preparing chuño, are obliged to wet their potatoes in order to make them freeze.