INTRODUCTION 6 



governed by the moisture supply. Its altitude is generally lower on the 

 western sides of the mountains which receive the heavier rainfall and higher 

 on the dry eastern sides. The difference is a thousand feet in some cases. 



A zone of Douglas fir (Pseudotsuga taxifolia) lies above the pine zone. The 

 usefulness of the Douglas fir ring record equals that of the pine, especially 

 in trees that grow in the transitional area along its lower edge where it mingles 

 with the pine. Firs extend downward in favorable canyons and shady slopes 

 almost as far as the yellow pine, and their ring records are superb in such 

 places. Mingling with the yellow pine at the lower edges of its zone is a 

 hard pine, the pinyon (Pinus edulis), a tree adapted to a water supply less 

 than that required by the yellow pine. 



Below the pine and pinyon on the mountain slopes there stand the juni- 

 pers, the last outposts of the forests. They can survive on the scanty water 

 supply and so cover large areas at 4000 to 5000 feet. There are several 

 species, Juniperus Utahensea, J. monosperma, J. pachyphlcea, and J. scopul- 

 orum, not very different in their several ring types and each rarely giving a 

 specimen whose rings are readable enough for dating purposes. 



West of the Arizona forested areas there lies the valley of the Big 

 Colorado, a large, exceedingly dry area which might be called the climatic 

 shadow of the higher mountain ranges of southern California whose westerly 

 faces get a substantial rainfall. These ranges are the southern extension of 

 the Sierra Nevadas that extend along the east side of California. Near 

 the ocean there is a low coast range and between the coast range and the 

 Sierra Nevadas there is the large, dry, interior San Joaquin Valley. The 

 Sierra Nevadas form a high rampart effectually intercepting the rain-bear- 

 ing winds that come in from the Pacific. In a number of favorable spots 

 upon these mountains there are found the giant sequoias (Sequoia gigantea) 

 at elevations of 5000 to 7000 feet. These magnificent trees have a remark- 

 able capacity of withstanding the attacks of pests and fire and by strongly 

 tapering shape maintain with extraordinary strength isolated positions on 

 fairly exposed ridges. They gather together in large numbers in the inter- 

 vening basins which are quite commonly swampy. In this environment they 

 show more resemblance to the coast redwoods at far lower levels. In 1924 

 it was ascertained that the giant sequoias in the various groves from 

 Springville on the south to Calaveras on the north have strong cross-dating char- 

 acters. It was found that practically any ring sequence of a few hundred years 

 may be dated in terms of the standard sequences developed in the King's 

 River region. However, this cross-dating between trees is far more striking 

 in the southerly groves, King's River area, Sequoia National Park, and Spring- 

 ville. The identification of the date of a ring is easily done in trees grow- 

 ing on the uplands and midlands, but becomes difficult in the basins where 

 a continuous water supply permits the trees to have an increased rate of 

 growth and great regularity from year to year. 



While it is true that our chief studies have been done in the Colorado 

 Plateau area, the enormous age of the big sequoias and their cross-dating 



