THE CURVE OF THE BIG TREES. 141 



will be carried back farther and farther; yet for the present, and probably for a long time 

 to come, the curve of the Sequoia wa&hingtoniana is likely to be the most important of 

 all hnes of evidence as to the cUmate of the last 2,000 to 3,000 years. We may add that it 

 is likely to be one of the most important lines of evidence as to the climate of the future, 

 for it will probably give us more knowledge of prolonged cycles and more data for use in 

 the determination of the causes of climatic changes than will any other individual group 

 of facts. Hence it behooves us to treat the subject with the utmost care and to use every 

 possible means of obtaining high accuracy. 



The Sequoia icashingloniana, as is well known, is one of two species of redwood, a genus 

 which grows in California, and nowhere else. The other species is the Sequoia seviper- 

 virens, or coast redwood, which possesses many of the qualities of its cousin, the giant 

 redwood, but attains neither such great age nor such great size. It flourishes in the Coast 

 Range of California, from a point about 100 miles south of San Francisco to the northern 

 part of the State. It is never found at any great distance from the sea, for its habitat is 

 limited to places on the western slope of the mountains, where summer fogs keep the air 

 moist and where the precipitation is heavy because the winds from the west are there first 

 compelled to rise. The other redwood, the giant species with which we are mainly con- 

 cerned, grows in a similar environment among the Sierra Nevadas. Its habitat is hmited 

 to a narrow strip 250 miles long, beginning near latitude 36°, in the mountains east of 

 Portersville, and extending northwest as far as latitude 39°, west of Lake Tahoe. The 

 trees are found only near the western edge of the mountains, at an altitude which rarely 

 falls below 5,000 feet even at the northern limits, and rarely rises above 7,000 even in the 

 south. In any given locahty the range is almost never more than 1,000 feet. 



The giant sequoia is strictly limited to a narrow band of abundant precipitation. As 

 the westerly winds come from the Pacific Ocean they first cross the coastal belt of cold 

 water which prevails along much of the California shore. There they are so chilled, 

 especially in summer, that their moisture is condensed into fogs. Then they rise over the 

 Coast Range, and in so doing are once more cooled and obliged to give up moisture in the 

 form of rain. These two sources of moisture make possible the existence of the Sequoia 

 sempervirens, but only in its own special, narrow strip. 



Proceeding eastward the winds descend into the inner valley of California, and by so 

 doing become warm and capable of holding much moisture. Hence the valley is dry, 

 especially on the west side, where the winds first descend. Farther eastward the air is 

 once more forced to rise by the Sierras. At first it does not give up much moisture, because 

 it has akeady lost so much in crossing the Coast Range. Only when it gets to an elevation 

 higher than that reached in crossing those mountains does condensation begin to take 

 place on a large scale. Thereafter precipitation increases rapidly for 2,000 to 3,000 feet, 

 after which it begins to decrease. The decrease is due partly to the fact that after a certain 

 point the actual amount of moisture which the cooled air is capable of holding becomes 

 shght, and a large amount of cooling is necessary in order to cause its precipitation, and 

 partly because after a height of 6,000 to 7,000 feet is attained the mountains no longer 

 rise steeply, so that the cooUng of the air is less rapid than on the front of the mountains. 

 These various conditions give rise to a narrow belt of heavy rainfall with drier areas on 

 either side, and in this belt alone the giant redwood flourishes. Along with it grow pines 

 and cedars, which are able also to grow at both higher and lower altitudes than the sequoia. 

 Another common tree is the white fir, which, with the Douglas fir, is found in abundance 

 not only with the sequoia, but in places too high and cold for it. Bushes as well as great 

 trees abound in the well-watered sequoia zone, and some, like the azalea, seem to be almost 

 as particular about their location as are the Big Trees. The azaleas' white flowers, tinged 

 with orange and pink, are often baiiked in great masses in the bottoms of the same moist 

 valleys where the sequoia dwells. 



