TREE RECORDS! GEOGRAPHICAL DISTRIBUTION 67 



rises gently to the States on the north. On this slope the great 

 Black Mesa has large cedar forests, with pines in the canyons and along 

 the northern edges. Then to the east is the Chin-lee Valley, and east 

 of that, on the border between Arizona and New Mexico, is the range 

 called Chuskas on many maps, with a southern part called the Lukai- 

 chukais. These carry extensive pine forests. The next pine-covered 

 range is a hundred miles east and forms the western boundary of the 

 Rio Grande Valley. This range has Mount Taylor at its southern 

 end and the Jemez Mountains west of Santa Fe. Chaco Canyon is 

 in the large area between the Chuskas and the Jemez Mountains. 

 It is surrounded by mesas which probably once held pine forests, but 

 the mountains just named are higher and its rainfall is small. East of 

 the Rio Grande Valley the big masses of the Rocky Mountains begin. 



WESTERN PINE GROUPS 



Statistics — The whole number of tree records minutely examined 

 up to date is about 1,100, and the total number of rings is close to 

 210,000. Of these, about 175,000 have been dated and measured. 

 The extensive failures to date the coast redwoods are largely responsible 

 for this difference between rings examined and rings measured, and 

 many of the groups have had a small proportion of the trees which 

 could not be dated. The number of trees included in the 42 groups 

 whose cycles are studied below is 305 and the number of rings dated 

 and measured is 52,400. These trees are practically all western yellow 

 pines, with a few Douglas firs here and there. 



Zone statistics — The 42 groups are divided into three zones: 

 (1) the interior or Arizona zone, where this study began and has had 

 the greatest extension; there are 14 groups in this zone, with 104 

 trees and 21,210 measures; (2) the eastern or Rocky Mountain zone 

 has 15 groups of 82 trees and 14,135 measures; and (3) the western or 

 coast zone has 119 trees in 13 groups, with 17,055 measures. 



Miscellaneous groups — A number of other groups not included 

 in the subsequent discussion of cycles follow the western pine groups. 

 They consist of groups of different kinds of trees, groups of good trees 

 which did not have enough material, such as the Raton and Pecos 

 groups of yellow pines with only one record each, of trees which could 

 not be dated, such as the coast redwood, and of groups from distant 

 localities. 



Group treatment — In the 42 western cycle groups only the individ- 

 uals are used which can be dated and also only those parts of each 

 individual which can be dated with certainty. In nearly every group 

 the curve of each individual tree has been standardized as described 

 in a previous chapter. Thus the different trees in a group have equal 

 weight and the age effect in the trees is largely removed. 



