74 CLIMATIC CYCLES AND TREE-GROWTH 



Thus the bold, pine-covered headlands of rock overlooking southern 

 Arizona differ in topography from the Flagstaff region, and it seemed 

 worth while to get a group of borings in such a locality. This was 

 easily done in a motor trip from Tucson to Flagstaff, on which I was 

 assisted by Mr. T. J. Randolph. The borings were made on August 

 26, 1922, two of them at 6,000 feet elevation, near the fork in the 

 highway between Pine and Strawberry, where the road to Flagstaff 

 starts up the big grade. These were numbered 91 and 92 in the Flag- 

 staff series and form the group RL. Two other borings were made 

 at the top of the Rim, where the elevation is 7,000 feet. These were 

 numbered 93 and 94 and constitute the present group RH. It was 

 intended to include all of these four in one group, but the two locations 

 proved so different in their effect on ring-type that it was thought 

 best to separate the pairs. The individuals of each pair agree finely. 

 Mr. Hawkins measured these four cores by auto-plot method. They 

 were then completely rechecked by the writer and individually stand- 

 ardized. The tables and curves were done by Mr. Austin. The curve 

 of the Upper Rim group, 1697 to 1921, smoothed by graphic Hann, 

 and shown in part in figure 4, is very complacent, and has only moder- 

 ate similarity to the typical Flagstaff curve. Its cycles, however, 

 keep it in the Arizona zone, for they are as follows: 14.7, 19.9 (3), 

 and 37 (2). 



LOWER RIM GROUP (RL) 



This group, as described in connection with the preceding, con- 

 sists of two increment-cores collected August 26, 1922, near the fork 

 in the road at the foot of the long Strawberry grade. The eleva- 

 tion is 6,000 feet. Its location is a south exposure with the great 

 thousand-foot wall of the Rim immediately to the north and a low, 

 flaMopped mesa "island" close to the south, standing up a few 

 hundred feet. The curve, 1770 to 1921, smoothed by a graphic Hann, 

 is shown in figure 4. Its striking variations resemble a shadow effect 

 like that in the SH group, which it minutely resembles. In fact, the 

 remarkable likeness between this curve and those of FLU, FV, SH, NE, 

 GC, and J groups puts this collection of groups in a distinctive homo- 

 geneous class whose locus extends at least from the Grand Canyon to the 

 Rim, a distance of about 150 miles. The RL cycles are 10.1, 12, 20.1 

 (3), 23.7, 27.6, and 38 (2, oc. -J). The absence of 14 years makes it 

 resemble the cycle of the Rocky Mountain zone, but as 14.4 did appear 

 in good form in one of the three analyses, its place in the Arizona zone 



is justified. 



CIBECUE GROUP (J) 



The Cibecue group of five increment-borings was collected on 

 July 23 and 24, 1920. The area included in this group extends from 

 the store on Grasshopper Creek (15 miles west of Cibecue Creek store) 

 to the small creek about a mile east. This is some 20 miles south of 



