76 CLIMATIC CYCLES AND TREE-GROWTH 



are given in some detail, because this group, while internally very- 

 satisfactory, is as a whole the most discordant in the entire Arizona 

 area, both in cross-identification of rings and in comparison between 

 smoothed curves. The SC specimens were measured part by auto- 

 plot and part by long-plot method. Individual trees were standard- 

 ized. The final curve, 1567 to 1919, shows a very limited resemblance 

 to curves in the Flagstaff area. After being smoothed by graphic 

 Hann, it shows many reversals of Flagstaff growth, for example, the 

 years near 1630, 1670, 1730, 1847, and 1880 have big growth instead of 

 small. The part since 1750 is given in figure 4. The cycles are 7.5, 

 9.2 (oc. £), 11.3, 17.4 (2), 22.9, and 34.7 (3, oc. £). The presence 

 of 11.3 and 17.4 gives it a resemblance to the Rocky Mountain zone 

 which incidentally has a number of reversals compared to Arizona. 



SANTA RITA GROUP (SR) 



The Santa Ritas, 9,400 feet in elevation, are 50 miles due south of 

 the Catalinas and form a massive mountain boundary on the east 

 side of the Santa Cruz Valley south of Tucson. The mountain slopes 

 are steep and the summit itself forms an upstanding monument of 

 rock 500 feet high, very striking in appearance. The pines cover the 

 upper parts of the mountain, but favor the north-facing canyons 

 where the snow lingers. Some Mexican species of pine are found here, 

 but they closely resemble the western yellow pine. A group of 10 

 borings was collected in the upper parts of White House Canyon, the 

 summer-resort region, on May 2, 1921, but these could not be dated, 

 as the doubling of rings by the pronounced summer rains made the 

 annual character very uncertain, a summer condition much more 

 pronounced here than in northern Arizona. So a second group of 6 

 borings was made December 22, 1921, at higher levels, that is, from 

 7,500 to 8,700 feet, of which all but one were usable. In this collection 

 I was assisted by Mr. M. S. Lankford. In a recent review it was 

 noted that the Santa Rita tree-records have the intensely small 

 Flagstaff years, 1847, 1902, 1904, and so forth, but are erratic within 

 the group, omissions and change of size making cross-identification 

 very laborious. 



Each of the five trees was standardized and the resulting average 

 curve, 1670 to 1921, smoothed by a graphic Hann, as shown from 1750 

 in figure 4. It resembles both the Flagstaff and the Catalina records. 

 Its minute details confirm the dating of the Catalina specimens, which 

 were at first held in considerable doubt. The cycles are 7.5, 11.2, 

 14.4 (3, oc. $), 23.0 (3), and 27.4 (oc. £). This is distinctly of the 

 Coast type. On the whole, it will not be surprising if these southern 

 island mountains are influenced by some climatic situation distinctly 

 different from the northern Arizona plateau area. 



